Fixed #470 -- Added support for database defaults on fields.

Special thanks to Hannes Ljungberg for finding multiple implementation
gaps.

Thanks also to Simon Charette, Adam Johnson, and Mariusz Felisiak for
reviews.

32 files changed, 1089 insertions, 34 deletions

diff --git a/AUTHORS b/AUTHORS
index ea321038ac..291b5da657 100644
--- a/AUTHORS
+++ b/AUTHORS
@@ -587,6 +587,7 @@ answer newbie questions, and generally made Django that much better:
     lerouxb@gmail.com
     Lex Berezhny <lex@damoti.com>
     Liang Feng <hutuworm@gmail.com>
+    Lily Foote
     limodou
     Lincoln Smith <lincoln.smith@anu.edu.au>
     Liu Yijie <007gzs@gmail.com>
diff --git a/django/db/backends/base/features.py b/django/db/backends/base/features.py
index 11fa807c1b..11dd079110 100644
--- a/django/db/backends/base/features.py
+++ b/django/db/backends/base/features.py
@@ -201,6 +201,15 @@ class BaseDatabaseFeatures:
     # Does the backend require literal defaults, rather than parameterized ones?
     requires_literal_defaults = False
 
+    # Does the backend support functions in defaults?
+    supports_expression_defaults = True
+
+    # Does the backend support the DEFAULT keyword in insert queries?
+    supports_default_keyword_in_insert = True
+
+    # Does the backend support the DEFAULT keyword in bulk insert queries?
+    supports_default_keyword_in_bulk_insert = True
+
     # Does the backend require a connection reset after each material schema change?
     connection_persists_old_columns = False
 
@@ -361,6 +370,9 @@ class BaseDatabaseFeatures:
     # SQL template override for tests.aggregation.tests.NowUTC
     test_now_utc_template = None
 
+    # SQL to create a model instance using the database defaults.
+    insert_test_table_with_defaults = None
+
     # A set of dotted paths to tests in Django's test suite that are expected
     # to fail on this database.
     django_test_expected_failures = set()
diff --git a/django/db/backends/base/schema.py b/django/db/backends/base/schema.py
index 6b03450e2f..01b56151be 100644
--- a/django/db/backends/base/schema.py
+++ b/django/db/backends/base/schema.py
@@ -12,7 +12,7 @@ from django.db.backends.ddl_references import (
     Table,
 )
 from django.db.backends.utils import names_digest, split_identifier, truncate_name
-from django.db.models import Deferrable, Index
+from django.db.models import NOT_PROVIDED, Deferrable, Index
 from django.db.models.sql import Query
 from django.db.transaction import TransactionManagementError, atomic
 from django.utils import timezone
@@ -296,6 +296,12 @@ class BaseDatabaseSchemaEditor:
             yield self._comment_sql(field.db_comment)
         # Work out nullability.
         null = field.null
+        # Add database default.
+        if field.db_default is not NOT_PROVIDED:
+            default_sql, default_params = self.db_default_sql(field)
+            yield f"DEFAULT {default_sql}"
+            params.extend(default_params)
+            include_default = False
         # Include a default value, if requested.
         include_default = (
             include_default
@@ -400,6 +406,22 @@ class BaseDatabaseSchemaEditor:
         """
         return "%s"
 
+    def db_default_sql(self, field):
+        """Return the sql and params for the field's database default."""
+        from django.db.models.expressions import Value
+
+        sql = "%s" if isinstance(field.db_default, Value) else "(%s)"
+        query = Query(model=field.model)
+        compiler = query.get_compiler(connection=self.connection)
+        default_sql, params = compiler.compile(field.db_default)
+        if self.connection.features.requires_literal_defaults:
+            # Some databases doesn't support parameterized defaults (Oracle,
+            # SQLite). If this is the case, the individual schema backend
+            # should implement prepare_default().
+            default_sql %= tuple(self.prepare_default(p) for p in params)
+            params = []
+        return sql % default_sql, params
+
     @staticmethod
     def _effective_default(field):
         # This method allows testing its logic without a connection.
@@ -1025,6 +1047,21 @@ class BaseDatabaseSchemaEditor:
             )
             actions.append(fragment)
             post_actions.extend(other_actions)
+
+        if new_field.db_default is not NOT_PROVIDED:
+            if (
+                old_field.db_default is NOT_PROVIDED
+                or new_field.db_default != old_field.db_default
+            ):
+                actions.append(
+                    self._alter_column_database_default_sql(model, old_field, new_field)
+                )
+        elif old_field.db_default is not NOT_PROVIDED:
+            actions.append(
+                self._alter_column_database_default_sql(
+                    model, old_field, new_field, drop=True
+                )
+            )
         # When changing a column NULL constraint to NOT NULL with a given
         # default value, we need to perform 4 steps:
         #  1. Add a default for new incoming writes
@@ -1033,7 +1070,11 @@ class BaseDatabaseSchemaEditor:
         #  4. Drop the default again.
         # Default change?
         needs_database_default = False
-        if old_field.null and not new_field.null:
+        if (
+            old_field.null
+            and not new_field.null
+            and new_field.db_default is NOT_PROVIDED
+        ):
             old_default = self.effective_default(old_field)
             new_default = self.effective_default(new_field)
             if (
@@ -1051,9 +1092,9 @@ class BaseDatabaseSchemaEditor:
             if fragment:
                 null_actions.append(fragment)
         # Only if we have a default and there is a change from NULL to NOT NULL
-        four_way_default_alteration = new_field.has_default() and (
-            old_field.null and not new_field.null
-        )
+        four_way_default_alteration = (
+            new_field.has_default() or new_field.db_default is not NOT_PROVIDED
+        ) and (old_field.null and not new_field.null)
         if actions or null_actions:
             if not four_way_default_alteration:
                 # If we don't have to do a 4-way default alteration we can
@@ -1074,15 +1115,20 @@ class BaseDatabaseSchemaEditor:
                     params,
                 )
             if four_way_default_alteration:
+                if new_field.db_default is NOT_PROVIDED:
+                    default_sql = "%s"
+                    params = [new_default]
+                else:
+                    default_sql, params = self.db_default_sql(new_field)
                 # Update existing rows with default value
                 self.execute(
                     self.sql_update_with_default
                     % {
                         "table": self.quote_name(model._meta.db_table),
                         "column": self.quote_name(new_field.column),
-                        "default": "%s",
+                        "default": default_sql,
                     },
-                    [new_default],
+                    params,
                 )
                 # Since we didn't run a NOT NULL change before we need to do it
                 # now
@@ -1264,6 +1310,34 @@ class BaseDatabaseSchemaEditor:
             params,
         )
 
+    def _alter_column_database_default_sql(
+        self, model, old_field, new_field, drop=False
+    ):
+        """
+        Hook to specialize column database default alteration.
+
+        Return a (sql, params) fragment to add or drop (depending on the drop
+        argument) a default to new_field's column.
+        """
+        if drop:
+            sql = self.sql_alter_column_no_default
+            default_sql = ""
+            params = []
+        else:
+            sql = self.sql_alter_column_default
+            default_sql, params = self.db_default_sql(new_field)
+
+        new_db_params = new_field.db_parameters(connection=self.connection)
+        return (
+            sql
+            % {
+                "column": self.quote_name(new_field.column),
+                "type": new_db_params["type"],
+                "default": default_sql,
+            },
+            params,
+        )
+
     def _alter_column_type_sql(
         self, model, old_field, new_field, new_type, old_collation, new_collation
     ):
diff --git a/django/db/backends/mysql/features.py b/django/db/backends/mysql/features.py
index 9e17d33e93..0bb0f91f55 100644
--- a/django/db/backends/mysql/features.py
+++ b/django/db/backends/mysql/features.py
@@ -51,6 +51,7 @@ class DatabaseFeatures(BaseDatabaseFeatures):
     # COLLATE must be wrapped in parentheses because MySQL treats COLLATE as an
     # indexed expression.
     collate_as_index_expression = True
+    insert_test_table_with_defaults = "INSERT INTO {} () VALUES ()"
 
     supports_order_by_nulls_modifier = False
     order_by_nulls_first = True
@@ -342,3 +343,9 @@ class DatabaseFeatures(BaseDatabaseFeatures):
         if self.connection.mysql_is_mariadb:
             return self.connection.mysql_version >= (10, 5, 2)
         return True
+
+    @cached_property
+    def supports_expression_defaults(self):
+        if self.connection.mysql_is_mariadb:
+            return True
+        return self.connection.mysql_version >= (8, 0, 13)
diff --git a/django/db/backends/mysql/schema.py b/django/db/backends/mysql/schema.py
index 31829506c1..bfe5a2e805 100644
--- a/django/db/backends/mysql/schema.py
+++ b/django/db/backends/mysql/schema.py
@@ -209,11 +209,15 @@ class DatabaseSchemaEditor(BaseDatabaseSchemaEditor):
         self._create_missing_fk_index(model, fields=fields)
         return super()._delete_composed_index(model, fields, *args)
 
-    def _set_field_new_type_null_status(self, field, new_type):
+    def _set_field_new_type(self, field, new_type):
         """
-        Keep the null property of the old field. If it has changed, it will be
-        handled separately.
+        Keep the NULL and DEFAULT properties of the old field. If it has
+        changed, it will be handled separately.
         """
+        if field.db_default is not NOT_PROVIDED:
+            default_sql, params = self.db_default_sql(field)
+            default_sql %= tuple(self.quote_value(p) for p in params)
+            new_type += f" DEFAULT {default_sql}"
         if field.null:
             new_type += " NULL"
         else:
@@ -223,7 +227,7 @@ class DatabaseSchemaEditor(BaseDatabaseSchemaEditor):
     def _alter_column_type_sql(
         self, model, old_field, new_field, new_type, old_collation, new_collation
     ):
-        new_type = self._set_field_new_type_null_status(old_field, new_type)
+        new_type = self._set_field_new_type(old_field, new_type)
         return super()._alter_column_type_sql(
             model, old_field, new_field, new_type, old_collation, new_collation
         )
@@ -242,7 +246,7 @@ class DatabaseSchemaEditor(BaseDatabaseSchemaEditor):
         return field_db_params["check"]
 
     def _rename_field_sql(self, table, old_field, new_field, new_type):
-        new_type = self._set_field_new_type_null_status(old_field, new_type)
+        new_type = self._set_field_new_type(old_field, new_type)
         return super()._rename_field_sql(table, old_field, new_field, new_type)
 
     def _alter_column_comment_sql(self, model, new_field, new_type, new_db_comment):
@@ -252,3 +256,18 @@ class DatabaseSchemaEditor(BaseDatabaseSchemaEditor):
     def _comment_sql(self, comment):
         comment_sql = super()._comment_sql(comment)
         return f" COMMENT {comment_sql}"
+
+    def _alter_column_null_sql(self, model, old_field, new_field):
+        if new_field.db_default is NOT_PROVIDED:
+            return super()._alter_column_null_sql(model, old_field, new_field)
+
+        new_db_params = new_field.db_parameters(connection=self.connection)
+        type_sql = self._set_field_new_type(new_field, new_db_params["type"])
+        return (
+            "MODIFY %(column)s %(type)s"
+            % {
+                "column": self.quote_name(new_field.column),
+                "type": type_sql,
+            },
+            [],
+        )
diff --git a/django/db/backends/oracle/features.py b/django/db/backends/oracle/features.py
index 05dc552a98..2ef9e4300c 100644
--- a/django/db/backends/oracle/features.py
+++ b/django/db/backends/oracle/features.py
@@ -32,6 +32,7 @@ class DatabaseFeatures(BaseDatabaseFeatures):
     atomic_transactions = False
     nulls_order_largest = True
     requires_literal_defaults = True
+    supports_default_keyword_in_bulk_insert = False
     closed_cursor_error_class = InterfaceError
     bare_select_suffix = " FROM DUAL"
     # Select for update with limit can be achieved on Oracle, but not with the
@@ -130,6 +131,9 @@ class DatabaseFeatures(BaseDatabaseFeatures):
         "annotations.tests.NonAggregateAnnotationTestCase."
         "test_custom_functions_can_ref_other_functions",
     }
+    insert_test_table_with_defaults = (
+        "INSERT INTO {} VALUES (DEFAULT, DEFAULT, DEFAULT)"
+    )
 
     @cached_property
     def introspected_field_types(self):
diff --git a/django/db/backends/oracle/introspection.py b/django/db/backends/oracle/introspection.py
index 5d1e3e6761..c4a734f7ec 100644
--- a/django/db/backends/oracle/introspection.py
+++ b/django/db/backends/oracle/introspection.py
@@ -156,7 +156,7 @@ class DatabaseIntrospection(BaseDatabaseIntrospection):
         field_map = {
             column: (
                 display_size,
-                default if default != "NULL" else None,
+                default.rstrip() if default and default != "NULL" else None,
                 collation,
                 is_autofield,
                 is_json,
diff --git a/django/db/backends/oracle/schema.py b/django/db/backends/oracle/schema.py
index 0d70522a2a..c8dd64650f 100644
--- a/django/db/backends/oracle/schema.py
+++ b/django/db/backends/oracle/schema.py
@@ -198,7 +198,9 @@ class DatabaseSchemaEditor(BaseDatabaseSchemaEditor):
         return self.normalize_name(for_name + "_" + suffix)
 
     def prepare_default(self, value):
-        return self.quote_value(value)
+        # Replace % with %% as %-formatting is applied in
+        # FormatStylePlaceholderCursor._fix_for_params().
+        return self.quote_value(value).replace("%", "%%")
 
     def _field_should_be_indexed(self, model, field):
         create_index = super()._field_should_be_indexed(model, field)
diff --git a/django/db/backends/postgresql/features.py b/django/db/backends/postgresql/features.py
index 732b30b0a4..29b6a4f6c5 100644
--- a/django/db/backends/postgresql/features.py
+++ b/django/db/backends/postgresql/features.py
@@ -76,6 +76,7 @@ class DatabaseFeatures(BaseDatabaseFeatures):
         "swedish_ci": "sv-x-icu",
     }
     test_now_utc_template = "STATEMENT_TIMESTAMP() AT TIME ZONE 'UTC'"
+    insert_test_table_with_defaults = "INSERT INTO {} DEFAULT VALUES"
 
     django_test_skips = {
         "opclasses are PostgreSQL only.": {
diff --git a/django/db/backends/sqlite3/features.py b/django/db/backends/sqlite3/features.py
index 7dd1c39702..f471b72cb2 100644
--- a/django/db/backends/sqlite3/features.py
+++ b/django/db/backends/sqlite3/features.py
@@ -59,6 +59,8 @@ class DatabaseFeatures(BaseDatabaseFeatures):
             PRIMARY KEY(column_1, column_2)
         )
     """
+    insert_test_table_with_defaults = 'INSERT INTO {} ("null") VALUES (1)'
+    supports_default_keyword_in_insert = False
 
     @cached_property
     def django_test_skips(self):
diff --git a/django/db/backends/sqlite3/schema.py b/django/db/backends/sqlite3/schema.py
index 2ca9a01855..46ba07092d 100644
--- a/django/db/backends/sqlite3/schema.py
+++ b/django/db/backends/sqlite3/schema.py
@@ -6,7 +6,7 @@ from django.db import NotSupportedError
 from django.db.backends.base.schema import BaseDatabaseSchemaEditor
 from django.db.backends.ddl_references import Statement
 from django.db.backends.utils import strip_quotes
-from django.db.models import UniqueConstraint
+from django.db.models import NOT_PROVIDED, UniqueConstraint
 from django.db.transaction import atomic
 
 
@@ -233,9 +233,13 @@ class DatabaseSchemaEditor(BaseDatabaseSchemaEditor):
         if create_field:
             body[create_field.name] = create_field
             # Choose a default and insert it into the copy map
-            if not create_field.many_to_many and create_field.concrete:
+            if (
+                create_field.db_default is NOT_PROVIDED
+                and not create_field.many_to_many
+                and create_field.concrete
+            ):
                 mapping[create_field.column] = self.prepare_default(
-                    self.effective_default(create_field),
+                    self.effective_default(create_field)
                 )
         # Add in any altered fields
         for alter_field in alter_fields:
@@ -244,9 +248,13 @@ class DatabaseSchemaEditor(BaseDatabaseSchemaEditor):
             mapping.pop(old_field.column, None)
             body[new_field.name] = new_field
             if old_field.null and not new_field.null:
+                if new_field.db_default is NOT_PROVIDED:
+                    default = self.prepare_default(self.effective_default(new_field))
+                else:
+                    default, _ = self.db_default_sql(new_field)
                 case_sql = "coalesce(%(col)s, %(default)s)" % {
                     "col": self.quote_name(old_field.column),
-                    "default": self.prepare_default(self.effective_default(new_field)),
+                    "default": default,
                 }
                 mapping[new_field.column] = case_sql
             else:
@@ -381,6 +389,8 @@ class DatabaseSchemaEditor(BaseDatabaseSchemaEditor):
 
     def add_field(self, model, field):
         """Create a field on a model."""
+        from django.db.models.expressions import Value
+
         # Special-case implicit M2M tables.
         if field.many_to_many and field.remote_field.through._meta.auto_created:
             self.create_model(field.remote_field.through)
@@ -394,6 +404,12 @@ class DatabaseSchemaEditor(BaseDatabaseSchemaEditor):
             # COLUMN statement because DROP DEFAULT is not supported in
             # ALTER TABLE.
             or self.effective_default(field) is not None
+            # Fields with non-constant defaults cannot by handled by ALTER
+            # TABLE ADD COLUMN statement.
+            or (
+                field.db_default is not NOT_PROVIDED
+                and not isinstance(field.db_default, Value)
+            )
         ):
             self._remake_table(model, create_field=field)
         else:
diff --git a/django/db/migrations/autodetector.py b/django/db/migrations/autodetector.py
index 23c97e5474..154ac44419 100644
--- a/django/db/migrations/autodetector.py
+++ b/django/db/migrations/autodetector.py
@@ -1040,6 +1040,7 @@ class MigrationAutodetector:
         preserve_default = (
             field.null
             or field.has_default()
+            or field.db_default is not models.NOT_PROVIDED
             or field.many_to_many
             or (field.blank and field.empty_strings_allowed)
             or (isinstance(field, time_fields) and field.auto_now)
@@ -1187,6 +1188,7 @@ class MigrationAutodetector:
                         old_field.null
                         and not new_field.null
                         and not new_field.has_default()
+                        and new_field.db_default is models.NOT_PROVIDED
                         and not new_field.many_to_many
                     ):
                         field = new_field.clone()
diff --git a/django/db/models/base.py b/django/db/models/base.py
index 344508e0e2..7aabe0b667 100644
--- a/django/db/models/base.py
+++ b/django/db/models/base.py
@@ -971,8 +971,10 @@ class Model(AltersData, metaclass=ModelBase):
             not raw
             and not force_insert
             and self._state.adding
-            and meta.pk.default
-            and meta.pk.default is not NOT_PROVIDED
+            and (
+                (meta.pk.default and meta.pk.default is not NOT_PROVIDED)
+                or (meta.pk.db_default and meta.pk.db_default is not NOT_PROVIDED)
+            )
         ):
             force_insert = True
         # If possible, try an UPDATE. If that doesn't update anything, do an INSERT.
diff --git a/django/db/models/expressions.py b/django/db/models/expressions.py
index d412e7657e..e1861759c4 100644
--- a/django/db/models/expressions.py
+++ b/django/db/models/expressions.py
@@ -176,6 +176,8 @@ class BaseExpression:
     filterable = True
     # Can the expression can be used as a source expression in Window?
     window_compatible = False
+    # Can the expression be used as a database default value?
+    allowed_default = False
 
     def __init__(self, output_field=None):
         if output_field is not None:
@@ -733,6 +735,10 @@ class CombinedExpression(SQLiteNumericMixin, Expression):
         c.rhs = rhs
         return c
 
+    @cached_property
+    def allowed_default(self):
+        return self.lhs.allowed_default and self.rhs.allowed_default
+
 
 class DurationExpression(CombinedExpression):
     def compile(self, side, compiler, connection):
@@ -804,6 +810,8 @@ class TemporalSubtraction(CombinedExpression):
 class F(Combinable):
     """An object capable of resolving references to existing query objects."""
 
+    allowed_default = False
+
     def __init__(self, name):
         """
         Arguments:
@@ -987,6 +995,10 @@ class Func(SQLiteNumericMixin, Expression):
         copy.extra = self.extra.copy()
         return copy
 
+    @cached_property
+    def allowed_default(self):
+        return all(expression.allowed_default for expression in self.source_expressions)
+
 
 @deconstructible(path="django.db.models.Value")
 class Value(SQLiteNumericMixin, Expression):
@@ -995,6 +1007,7 @@ class Value(SQLiteNumericMixin, Expression):
     # Provide a default value for `for_save` in order to allow unresolved
     # instances to be compiled until a decision is taken in #25425.
     for_save = False
+    allowed_default = True
 
     def __init__(self, value, output_field=None):
         """
@@ -1069,6 +1082,8 @@ class Value(SQLiteNumericMixin, Expression):
 
 
 class RawSQL(Expression):
+    allowed_default = True
+
     def __init__(self, sql, params, output_field=None):
         if output_field is None:
             output_field = fields.Field()
@@ -1110,6 +1125,13 @@ class Star(Expression):
         return "*", []
 
 
+class DatabaseDefault(Expression):
+    """Placeholder expression for the database default in an insert query."""
+
+    def as_sql(self, compiler, connection):
+        return "DEFAULT", []
+
+
 class Col(Expression):
     contains_column_references = True
     possibly_multivalued = False
@@ -1213,6 +1235,7 @@ class ExpressionList(Func):
 
 
 class OrderByList(Func):
+    allowed_default = False
     template = "ORDER BY %(expressions)s"
 
     def __init__(self, *expressions, **extra):
@@ -1270,6 +1293,10 @@ class ExpressionWrapper(SQLiteNumericMixin, Expression):
     def __repr__(self):
         return "{}({})".format(self.__class__.__name__, self.expression)
 
+    @property
+    def allowed_default(self):
+        return self.expression.allowed_default
+
 
 class NegatedExpression(ExpressionWrapper):
     """The logical negation of a conditional expression."""
@@ -1397,6 +1424,10 @@ class When(Expression):
             cols.extend(source.get_group_by_cols())
         return cols
 
+    @cached_property
+    def allowed_default(self):
+        return self.condition.allowed_default and self.result.allowed_default
+
 
 @deconstructible(path="django.db.models.Case")
 class Case(SQLiteNumericMixin, Expression):
@@ -1494,6 +1525,12 @@ class Case(SQLiteNumericMixin, Expression):
             return self.default.get_group_by_cols()
         return super().get_group_by_cols()
 
+    @cached_property
+    def allowed_default(self):
+        return self.default.allowed_default and all(
+            case_.allowed_default for case_ in self.cases
+        )
+
 
 class Subquery(BaseExpression, Combinable):
     """
diff --git a/django/db/models/fields/__init__.py b/django/db/models/fields/__init__.py
index 4416898d80..18b48c0e72 100644
--- a/django/db/models/fields/__init__.py
+++ b/django/db/models/fields/__init__.py
@@ -202,6 +202,7 @@ class Field(RegisterLookupMixin):
         validators=(),
         error_messages=None,
         db_comment=None,
+        db_default=NOT_PROVIDED,
     ):
         self.name = name
         self.verbose_name = verbose_name  # May be set by set_attributes_from_name
@@ -212,6 +213,13 @@ class Field(RegisterLookupMixin):
         self.remote_field = rel
         self.is_relation = self.remote_field is not None
         self.default = default
+        if db_default is not NOT_PROVIDED and not hasattr(
+            db_default, "resolve_expression"
+        ):
+            from django.db.models.expressions import Value
+
+            db_default = Value(db_default)
+        self.db_default = db_default
         self.editable = editable
         self.serialize = serialize
         self.unique_for_date = unique_for_date
@@ -263,6 +271,7 @@ class Field(RegisterLookupMixin):
         return [
             *self._check_field_name(),
             *self._check_choices(),
+            *self._check_db_default(**kwargs),
             *self._check_db_index(),
             *self._check_db_comment(**kwargs),
             *self._check_null_allowed_for_primary_keys(),
@@ -379,6 +388,39 @@ class Field(RegisterLookupMixin):
             )
         ]
 
+    def _check_db_default(self, databases=None, **kwargs):
+        from django.db.models.expressions import Value
+
+        if (
+            self.db_default is NOT_PROVIDED
+            or isinstance(self.db_default, Value)
+            or databases is None
+        ):
+            return []
+        errors = []
+        for db in databases:
+            if not router.allow_migrate_model(db, self.model):
+                continue
+            connection = connections[db]
+
+            if not getattr(self.db_default, "allowed_default", False) and (
+                connection.features.supports_expression_defaults
+            ):
+                msg = f"{self.db_default} cannot be used in db_default."
+                errors.append(checks.Error(msg, obj=self, id="fields.E012"))
+
+            if not (
+                connection.features.supports_expression_defaults
+                or "supports_expression_defaults"
+                in self.model._meta.required_db_features
+            ):
+                msg = (
+                    f"{connection.display_name} does not support default database "
+                    "values with expressions (db_default)."
+                )
+                errors.append(checks.Error(msg, obj=self, id="fields.E011"))
+        return errors
+
     def _check_db_index(self):
         if self.db_index not in (None, True, False):
             return [
@@ -558,6 +600,7 @@ class Field(RegisterLookupMixin):
             "null": False,
             "db_index": False,
             "default": NOT_PROVIDED,
+            "db_default": NOT_PROVIDED,
             "editable": True,
             "serialize": True,
             "unique_for_date": None,
@@ -876,7 +919,10 @@ class Field(RegisterLookupMixin):
     @property
     def db_returning(self):
         """Private API intended only to be used by Django itself."""
-        return False
+        return (
+            self.db_default is not NOT_PROVIDED
+            and connection.features.can_return_columns_from_insert
+        )
 
     def set_attributes_from_name(self, name):
         self.name = self.name or name
@@ -929,7 +975,13 @@ class Field(RegisterLookupMixin):
 
     def pre_save(self, model_instance, add):
         """Return field's value just before saving."""
-        return getattr(model_instance, self.attname)
+        value = getattr(model_instance, self.attname)
+        if not connection.features.supports_default_keyword_in_insert:
+            from django.db.models.expressions import DatabaseDefault
+
+            if isinstance(value, DatabaseDefault):
+                return self.db_default
+        return value
 
     def get_prep_value(self, value):
         """Perform preliminary non-db specific value checks and conversions."""
@@ -968,6 +1020,11 @@ class Field(RegisterLookupMixin):
                 return self.default
             return lambda: self.default
 
+        if self.db_default is not NOT_PROVIDED:
+            from django.db.models.expressions import DatabaseDefault
+
+            return DatabaseDefault
+
         if (
             not self.empty_strings_allowed
             or self.null
diff --git a/django/db/models/functions/comparison.py b/django/db/models/functions/comparison.py
index de7eef4cdc..108d904712 100644
--- a/django/db/models/functions/comparison.py
+++ b/django/db/models/functions/comparison.py
@@ -105,6 +105,7 @@ class Coalesce(Func):
 class Collate(Func):
     function = "COLLATE"
     template = "%(expressions)s %(function)s %(collation)s"
+    allowed_default = False
     # Inspired from
     # https://www.postgresql.org/docs/current/sql-syntax-lexical.html#SQL-SYNTAX-IDENTIFIERS
     collation_re = _lazy_re_compile(r"^[\w\-]+$")
diff --git a/django/db/models/lookups.py b/django/db/models/lookups.py
index 46ebe3f3a2..91342a864a 100644
--- a/django/db/models/lookups.py
+++ b/django/db/models/lookups.py
@@ -185,6 +185,10 @@ class Lookup(Expression):
             sql = f"CASE WHEN {sql} THEN 1 ELSE 0 END"
         return sql, params
 
+    @cached_property
+    def allowed_default(self):
+        return self.lhs.allowed_default and self.rhs.allowed_default
+
 
 class Transform(RegisterLookupMixin, Func):
     """
diff --git a/django/db/models/query.py b/django/db/models/query.py
index 56ad4d5c20..a5b0f464a9 100644
--- a/django/db/models/query.py
+++ b/django/db/models/query.py
@@ -654,10 +654,19 @@ class QuerySet(AltersData):
         return await sync_to_async(self.create)(**kwargs)
 
     def _prepare_for_bulk_create(self, objs):
+        from django.db.models.expressions import DatabaseDefault
+
+        connection = connections[self.db]
         for obj in objs:
             if obj.pk is None:
                 # Populate new PK values.
                 obj.pk = obj._meta.pk.get_pk_value_on_save(obj)
+            if not connection.features.supports_default_keyword_in_bulk_insert:
+                for field in obj._meta.fields:
+                    value = getattr(obj, field.attname)
+                    if isinstance(value, DatabaseDefault):
+                        setattr(obj, field.attname, field.db_default)
+
             obj._prepare_related_fields_for_save(operation_name="bulk_create")
 
     def _check_bulk_create_options(
diff --git a/docs/ref/checks.txt b/docs/ref/checks.txt
index 9e350a3ff3..df0adbef63 100644
--- a/docs/ref/checks.txt
+++ b/docs/ref/checks.txt
@@ -175,6 +175,9 @@ Model fields
   ``choices`` (``<count>`` characters).
 * **fields.E010**: ``<field>`` default should be a callable instead of an
   instance so that it's not shared between all field instances.
+* **fields.E011**: ``<database>`` does not support default database values with
+  expressions (``db_default``).
+* **fields.E012**: ``<expression>`` cannot be used in ``db_default``.
 * **fields.E100**: ``AutoField``\s must set primary_key=True.
 * **fields.E110**: ``BooleanField``\s do not accept null values. *This check
   appeared before support for null values was added in Django 2.1.*
diff --git a/docs/ref/models/expressions.txt b/docs/ref/models/expressions.txt
index 52a1022771..50560dfa9b 100644
--- a/docs/ref/models/expressions.txt
+++ b/docs/ref/models/expressions.txt
@@ -996,6 +996,13 @@ calling the appropriate methods on the wrapped expression.
 
 .. class:: Expression
 
+    .. attribute:: allowed_default
+
+        .. versionadded:: 5.0
+
+        Tells Django that this expression can be used in
+        :attr:`Field.db_default`. Defaults to ``False``.
+
     .. attribute:: contains_aggregate
 
         Tells Django that this expression contains an aggregate and that a
diff --git a/docs/ref/models/fields.txt b/docs/ref/models/fields.txt
index 27b87c1f53..344cc45280 100644
--- a/docs/ref/models/fields.txt
+++ b/docs/ref/models/fields.txt
@@ -351,6 +351,38 @@ looking at your Django code. For example::
         db_comment="Date and time when the article was published",
     )
 
+``db_default``
+--------------
+
+.. versionadded:: 5.0
+
+.. attribute:: Field.db_default
+
+The database-computed default value for this field. This can be a literal value
+or a database function, such as :class:`~django.db.models.functions.Now`::
+
+    created = models.DateTimeField(db_default=Now())
+
+More complex expressions can be used, as long as they are made from literals
+and database functions::
+
+    month_due = models.DateField(
+        db_default=TruncMonth(
+            Now() + timedelta(days=90),
+            output_field=models.DateField(),
+        )
+    )
+
+Database defaults cannot reference other fields or models. For example, this is
+invalid::
+
+    end = models.IntegerField(db_default=F("start") + 50)
+
+If both ``db_default`` and :attr:`Field.default` are set, ``default`` will take
+precedence when creating instances in Python code. ``db_default`` will still be
+set at the database level and will be used when inserting rows outside of the
+ORM or when adding a new field in a migration.
+
 ``db_index``
 ------------
 
@@ -408,6 +440,9 @@ The default value is used when new model instances are created and a value
 isn't provided for the field. When the field is a primary key, the default is
 also used when the field is set to ``None``.
 
+The default value can also be set at the database level with
+:attr:`Field.db_default`.
+
 ``editable``
 ------------
 
diff --git a/docs/ref/models/instances.txt b/docs/ref/models/instances.txt
index d03b05577c..346ae55130 100644
--- a/docs/ref/models/instances.txt
+++ b/docs/ref/models/instances.txt
@@ -541,7 +541,8 @@ You may have noticed Django database objects use the same ``save()`` method
 for creating and changing objects. Django abstracts the need to use ``INSERT``
 or ``UPDATE`` SQL statements. Specifically, when you call ``save()`` and the
 object's primary key attribute does **not** define a
-:attr:`~django.db.models.Field.default`, Django follows this algorithm:
+:attr:`~django.db.models.Field.default` or
+:attr:`~django.db.models.Field.db_default`, Django follows this algorithm:
 
 * If the object's primary key attribute is set to a value that evaluates to
   ``True`` (i.e., a value other than ``None`` or the empty string), Django
@@ -551,9 +552,10 @@ object's primary key attribute does **not** define a
   exist in the database), Django executes an ``INSERT``.
 
 If the object's primary key attribute defines a
-:attr:`~django.db.models.Field.default` then Django executes an ``UPDATE`` if
-it is an existing model instance and primary key is set to a value that exists
-in the database. Otherwise, Django executes an ``INSERT``.
+:attr:`~django.db.models.Field.default` or
+:attr:`~django.db.models.Field.db_default` then Django executes an ``UPDATE``
+if it is an existing model instance and primary key is set to a value that
+exists in the database. Otherwise, Django executes an ``INSERT``.
 
 The one gotcha here is that you should be careful not to specify a primary-key
 value explicitly when saving new objects, if you cannot guarantee the
@@ -570,6 +572,10 @@ which returns ``NULL``. In such cases it is possible to revert to the old
 algorithm by setting the :attr:`~django.db.models.Options.select_on_save`
 option to ``True``.
 
+.. versionchanged:: 5.0
+
+    The ``Field.db_default`` parameter was added.
+
 .. _ref-models-force-insert:
 
 Forcing an INSERT or UPDATE
diff --git a/docs/releases/5.0.txt b/docs/releases/5.0.txt
index f23f39b014..d40cd6a4f0 100644
--- a/docs/releases/5.0.txt
+++ b/docs/releases/5.0.txt
@@ -108,6 +108,21 @@ Can now be simplified to:
 per-project, per-field, or per-request basis. See
 :ref:`reusable-field-group-templates`.
 
+Database-computed default values
+--------------------------------
+
+The new :attr:`Field.db_default <django.db.models.Field.db_default>` parameter
+sets a database-computed default value. For example::
+
+    from django.db import models
+    from django.db.models.functions import Now, Pi
+
+
+    class MyModel(models.Model):
+        age = models.IntegerField(db_default=18)
+        created = models.DateTimeField(db_default=Now())
+        circumference = models.FloatField(db_default=2 * Pi())
+
 Minor features
 --------------
 
@@ -355,7 +370,16 @@ Database backend API
 This section describes changes that may be needed in third-party database
 backends.
 
-* ...
+* ``DatabaseFeatures.supports_expression_defaults`` should be set to ``False``
+  if the database doesn't support using database functions as defaults.
+
+* ``DatabaseFeatures.supports_default_keyword_in_insert`` should be set to
+  ``False`` if the database doesn't support the ``DEFAULT`` keyword in
+  ``INSERT`` queries.
+
+* ``DatabaseFeatures.supports_default_keyword_in_bulk insert`` should be set to
+  ``False`` if the database doesn't support the ``DEFAULT`` keyword in bulk
+  ``INSERT`` queries.
 
 Using ``create_defaults__exact`` may now be required with ``QuerySet.update_or_create()``
 -----------------------------------------------------------------------------------------
diff --git a/tests/basic/models.py b/tests/basic/models.py
index 59a6a8d67f..b71b60a213 100644
--- a/tests/basic/models.py
+++ b/tests/basic/models.py
@@ -49,5 +49,9 @@ class PrimaryKeyWithDefault(models.Model):
     uuid = models.UUIDField(primary_key=True, default=uuid.uuid4)
 
 
+class PrimaryKeyWithDbDefault(models.Model):
+    uuid = models.IntegerField(primary_key=True, db_default=1)
+
+
 class ChildPrimaryKeyWithDefault(PrimaryKeyWithDefault):
     pass
diff --git a/tests/basic/tests.py b/tests/basic/tests.py
index ea9228376c..3c2d1dead9 100644
--- a/tests/basic/tests.py
+++ b/tests/basic/tests.py
@@ -20,6 +20,7 @@ from .models import (
     ArticleSelectOnSave,
     ChildPrimaryKeyWithDefault,
     FeaturedArticle,
+    PrimaryKeyWithDbDefault,
     PrimaryKeyWithDefault,
     SelfRef,
 )
@@ -175,6 +176,11 @@ class ModelInstanceCreationTests(TestCase):
         with self.assertNumQueries(1):
             PrimaryKeyWithDefault().save()
 
+    def test_save_primary_with_db_default(self):
+        # An UPDATE attempt is skipped when a primary key has db_default.
+        with self.assertNumQueries(1):
+            PrimaryKeyWithDbDefault().save()
+
     def test_save_parent_primary_with_default(self):
         # An UPDATE attempt is skipped when an inherited primary key has
         # default.
diff --git a/tests/field_defaults/models.py b/tests/field_defaults/models.py
index b95005192a..5f9c38a5a4 100644
--- a/tests/field_defaults/models.py
+++ b/tests/field_defaults/models.py
@@ -12,6 +12,8 @@ field.
 from datetime import datetime
 
 from django.db import models
+from django.db.models.functions import Coalesce, ExtractYear, Now, Pi
+from django.db.models.lookups import GreaterThan
 
 
 class Article(models.Model):
@@ -20,3 +22,45 @@ class Article(models.Model):
 
     def __str__(self):
         return self.headline
+
+
+class DBArticle(models.Model):
+    """
+    Values or expressions can be passed as the db_default parameter to a field.
+    When the object is created without an explicit value passed in, the
+    database will insert the default value automatically.
+    """
+
+    headline = models.CharField(max_length=100, db_default="Default headline")
+    pub_date = models.DateTimeField(db_default=Now())
+
+    class Meta:
+        required_db_features = {"supports_expression_defaults"}
+
+
+class DBDefaults(models.Model):
+    both = models.IntegerField(default=1, db_default=2)
+    null = models.FloatField(null=True, db_default=1.1)
+
+
+class DBDefaultsFunction(models.Model):
+    number = models.FloatField(db_default=Pi())
+    year = models.IntegerField(db_default=ExtractYear(Now()))
+    added = models.FloatField(db_default=Pi() + 4.5)
+    multiple_subfunctions = models.FloatField(db_default=Coalesce(4.5, Pi()))
+    case_when = models.IntegerField(
+        db_default=models.Case(models.When(GreaterThan(2, 1), then=3), default=4)
+    )
+
+    class Meta:
+        required_db_features = {"supports_expression_defaults"}
+
+
+class DBDefaultsPK(models.Model):
+    language_code = models.CharField(primary_key=True, max_length=2, db_default="en")
+
+
+class DBDefaultsFK(models.Model):
+    language_code = models.ForeignKey(
+        DBDefaultsPK, db_default="fr", on_delete=models.CASCADE
+    )
diff --git a/tests/field_defaults/tests.py b/tests/field_defaults/tests.py
index 19b05aa537..76d01f7a5a 100644
--- a/tests/field_defaults/tests.py
+++ b/tests/field_defaults/tests.py
@@ -1,8 +1,28 @@
 from datetime import datetime
+from math import pi
 
-from django.test import TestCase
+from django.db import connection
+from django.db.models import Case, F, FloatField, Value, When
+from django.db.models.expressions import (
+    Expression,
+    ExpressionList,
+    ExpressionWrapper,
+    Func,
+    OrderByList,
+    RawSQL,
+)
+from django.db.models.functions import Collate
+from django.db.models.lookups import GreaterThan
+from django.test import SimpleTestCase, TestCase, skipIfDBFeature, skipUnlessDBFeature
 
-from .models import Article
+from .models import (
+    Article,
+    DBArticle,
+    DBDefaults,
+    DBDefaultsFK,
+    DBDefaultsFunction,
+    DBDefaultsPK,
+)
 
 
 class DefaultTests(TestCase):
@@ -14,3 +34,171 @@ class DefaultTests(TestCase):
         self.assertIsInstance(a.id, int)
         self.assertEqual(a.headline, "Default headline")
         self.assertLess((now - a.pub_date).seconds, 5)
+
+    @skipUnlessDBFeature(
+        "can_return_columns_from_insert", "supports_expression_defaults"
+    )
+    def test_field_db_defaults_returning(self):
+        a = DBArticle()
+        a.save()
+        self.assertIsInstance(a.id, int)
+        self.assertEqual(a.headline, "Default headline")
+        self.assertIsInstance(a.pub_date, datetime)
+
+    @skipIfDBFeature("can_return_columns_from_insert")
+    @skipUnlessDBFeature("supports_expression_defaults")
+    def test_field_db_defaults_refresh(self):
+        a = DBArticle()
+        a.save()
+        a.refresh_from_db()
+        self.assertIsInstance(a.id, int)
+        self.assertEqual(a.headline, "Default headline")
+        self.assertIsInstance(a.pub_date, datetime)
+
+    def test_null_db_default(self):
+        obj1 = DBDefaults.objects.create()
+        if not connection.features.can_return_columns_from_insert:
+            obj1.refresh_from_db()
+        self.assertEqual(obj1.null, 1.1)
+
+        obj2 = DBDefaults.objects.create(null=None)
+        self.assertIsNone(obj2.null)
+
+    @skipUnlessDBFeature("supports_expression_defaults")
+    def test_db_default_function(self):
+        m = DBDefaultsFunction.objects.create()
+        if not connection.features.can_return_columns_from_insert:
+            m.refresh_from_db()
+        self.assertAlmostEqual(m.number, pi)
+        self.assertEqual(m.year, datetime.now().year)
+        self.assertAlmostEqual(m.added, pi + 4.5)
+        self.assertEqual(m.multiple_subfunctions, 4.5)
+
+    @skipUnlessDBFeature("insert_test_table_with_defaults")
+    def test_both_default(self):
+        create_sql = connection.features.insert_test_table_with_defaults
+        with connection.cursor() as cursor:
+            cursor.execute(create_sql.format(DBDefaults._meta.db_table))
+        obj1 = DBDefaults.objects.get()
+        self.assertEqual(obj1.both, 2)
+
+        obj2 = DBDefaults.objects.create()
+        self.assertEqual(obj2.both, 1)
+
+    def test_pk_db_default(self):
+        obj1 = DBDefaultsPK.objects.create()
+        if not connection.features.can_return_columns_from_insert:
+            # refresh_from_db() cannot be used because that needs the pk to
+            # already be known to Django.
+            obj1 = DBDefaultsPK.objects.get(pk="en")
+        self.assertEqual(obj1.pk, "en")
+        self.assertEqual(obj1.language_code, "en")
+
+        obj2 = DBDefaultsPK.objects.create(language_code="de")
+        self.assertEqual(obj2.pk, "de")
+        self.assertEqual(obj2.language_code, "de")
+
+    def test_foreign_key_db_default(self):
+        parent1 = DBDefaultsPK.objects.create(language_code="fr")
+        child1 = DBDefaultsFK.objects.create()
+        if not connection.features.can_return_columns_from_insert:
+            child1.refresh_from_db()
+        self.assertEqual(child1.language_code, parent1)
+
+        parent2 = DBDefaultsPK.objects.create()
+        if not connection.features.can_return_columns_from_insert:
+            # refresh_from_db() cannot be used because that needs the pk to
+            # already be known to Django.
+            parent2 = DBDefaultsPK.objects.get(pk="en")
+        child2 = DBDefaultsFK.objects.create(language_code=parent2)
+        self.assertEqual(child2.language_code, parent2)
+
+    @skipUnlessDBFeature(
+        "can_return_columns_from_insert", "supports_expression_defaults"
+    )
+    def test_case_when_db_default_returning(self):
+        m = DBDefaultsFunction.objects.create()
+        self.assertEqual(m.case_when, 3)
+
+    @skipIfDBFeature("can_return_columns_from_insert")
+    @skipUnlessDBFeature("supports_expression_defaults")
+    def test_case_when_db_default_no_returning(self):
+        m = DBDefaultsFunction.objects.create()
+        m.refresh_from_db()
+        self.assertEqual(m.case_when, 3)
+
+    @skipUnlessDBFeature("supports_expression_defaults")
+    def test_bulk_create_all_db_defaults(self):
+        articles = [DBArticle(), DBArticle()]
+        DBArticle.objects.bulk_create(articles)
+
+        headlines = DBArticle.objects.values_list("headline", flat=True)
+        self.assertSequenceEqual(headlines, ["Default headline", "Default headline"])
+
+    @skipUnlessDBFeature("supports_expression_defaults")
+    def test_bulk_create_all_db_defaults_one_field(self):
+        pub_date = datetime.now()
+        articles = [DBArticle(pub_date=pub_date), DBArticle(pub_date=pub_date)]
+        DBArticle.objects.bulk_create(articles)
+
+        headlines = DBArticle.objects.values_list("headline", "pub_date")
+        self.assertSequenceEqual(
+            headlines,
+            [
+                ("Default headline", pub_date),
+                ("Default headline", pub_date),
+            ],
+        )
+
+    @skipUnlessDBFeature("supports_expression_defaults")
+    def test_bulk_create_mixed_db_defaults(self):
+        articles = [DBArticle(), DBArticle(headline="Something else")]
+        DBArticle.objects.bulk_create(articles)
+
+        headlines = DBArticle.objects.values_list("headline", flat=True)
+        self.assertCountEqual(headlines, ["Default headline", "Something else"])
+
+    @skipUnlessDBFeature("supports_expression_defaults")
+    def test_bulk_create_mixed_db_defaults_function(self):
+        instances = [DBDefaultsFunction(), DBDefaultsFunction(year=2000)]
+        DBDefaultsFunction.objects.bulk_create(instances)
+
+        years = DBDefaultsFunction.objects.values_list("year", flat=True)
+        self.assertCountEqual(years, [2000, datetime.now().year])
+
+
+class AllowedDefaultTests(SimpleTestCase):
+    def test_allowed(self):
+        class Max(Func):
+            function = "MAX"
+
+        tests = [
+            Value(10),
+            Max(1, 2),
+            RawSQL("Now()", ()),
+            Value(10) + Value(7),  # Combined expression.
+            ExpressionList(Value(1), Value(2)),
+            ExpressionWrapper(Value(1), output_field=FloatField()),
+            Case(When(GreaterThan(2, 1), then=3), default=4),
+        ]
+        for expression in tests:
+            with self.subTest(expression=expression):
+                self.assertIs(expression.allowed_default, True)
+
+    def test_disallowed(self):
+        class Max(Func):
+            function = "MAX"
+
+        tests = [
+            Expression(),
+            F("field"),
+            Max(F("count"), 1),
+            Value(10) + F("count"),  # Combined expression.
+            ExpressionList(F("count"), Value(2)),
+            ExpressionWrapper(F("count"), output_field=FloatField()),
+            Collate(Value("John"), "nocase"),
+            OrderByList("field"),
+        ]
+        for expression in tests:
+            with self.subTest(expression=expression):
+                self.assertIs(expression.allowed_default, False)
diff --git a/tests/invalid_models_tests/test_ordinary_fields.py b/tests/invalid_models_tests/test_ordinary_fields.py
index 4e37c48286..e9e8a702e0 100644
--- a/tests/invalid_models_tests/test_ordinary_fields.py
+++ b/tests/invalid_models_tests/test_ordinary_fields.py
@@ -4,6 +4,7 @@ import uuid
 from django.core.checks import Error
 from django.core.checks import Warning as DjangoWarning
 from django.db import connection, models
+from django.db.models.functions import Coalesce, Pi
 from django.test import SimpleTestCase, TestCase, skipIfDBFeature, skipUnlessDBFeature
 from django.test.utils import isolate_apps, override_settings
 from django.utils.functional import lazy
@@ -1057,3 +1058,109 @@ class DbCommentTests(TestCase):
 
         errors = Model._meta.get_field("field").check(databases=self.databases)
         self.assertEqual(errors, [])
+
+
+@isolate_apps("invalid_models_tests")
+class InvalidDBDefaultTests(TestCase):
+    def test_db_default(self):
+        class Model(models.Model):
+            field = models.FloatField(db_default=Pi())
+
+        field = Model._meta.get_field("field")
+        errors = field.check(databases=self.databases)
+
+        if connection.features.supports_expression_defaults:
+            expected_errors = []
+        else:
+            msg = (
+                f"{connection.display_name} does not support default database values "
+                "with expressions (db_default)."
+            )
+            expected_errors = [Error(msg=msg, obj=field, id="fields.E011")]
+        self.assertEqual(errors, expected_errors)
+
+    def test_db_default_literal(self):
+        class Model(models.Model):
+            field = models.IntegerField(db_default=1)
+
+        field = Model._meta.get_field("field")
+        errors = field.check(databases=self.databases)
+        self.assertEqual(errors, [])
+
+    def test_db_default_required_db_features(self):
+        class Model(models.Model):
+            field = models.FloatField(db_default=Pi())
+
+            class Meta:
+                required_db_features = {"supports_expression_defaults"}
+
+        field = Model._meta.get_field("field")
+        errors = field.check(databases=self.databases)
+        self.assertEqual(errors, [])
+
+    def test_db_default_expression_invalid(self):
+        expression = models.F("field_name")
+
+        class Model(models.Model):
+            field = models.FloatField(db_default=expression)
+
+        field = Model._meta.get_field("field")
+        errors = field.check(databases=self.databases)
+
+        if connection.features.supports_expression_defaults:
+            msg = f"{expression} cannot be used in db_default."
+            expected_errors = [Error(msg=msg, obj=field, id="fields.E012")]
+        else:
+            msg = (
+                f"{connection.display_name} does not support default database values "
+                "with expressions (db_default)."
+            )
+            expected_errors = [Error(msg=msg, obj=field, id="fields.E011")]
+        self.assertEqual(errors, expected_errors)
+
+    def test_db_default_expression_required_db_features(self):
+        expression = models.F("field_name")
+
+        class Model(models.Model):
+            field = models.FloatField(db_default=expression)
+
+            class Meta:
+                required_db_features = {"supports_expression_defaults"}
+
+        field = Model._meta.get_field("field")
+        errors = field.check(databases=self.databases)
+
+        if connection.features.supports_expression_defaults:
+            msg = f"{expression} cannot be used in db_default."
+            expected_errors = [Error(msg=msg, obj=field, id="fields.E012")]
+        else:
+            expected_errors = []
+        self.assertEqual(errors, expected_errors)
+
+    @skipUnlessDBFeature("supports_expression_defaults")
+    def test_db_default_combined_invalid(self):
+        expression = models.Value(4.5) + models.F("field_name")
+
+        class Model(models.Model):
+            field = models.FloatField(db_default=expression)
+
+        field = Model._meta.get_field("field")
+        errors = field.check(databases=self.databases)
+
+        msg = f"{expression} cannot be used in db_default."
+        expected_error = Error(msg=msg, obj=field, id="fields.E012")
+        self.assertEqual(errors, [expected_error])
+
+    @skipUnlessDBFeature("supports_expression_defaults")
+    def test_db_default_function_arguments_invalid(self):
+        expression = Coalesce(models.Value(4.5), models.F("field_name"))
+
+        class Model(models.Model):
+            field = models.FloatField(db_default=expression)
+
+        field = Model._meta.get_field("field")
+        errors = field.check(databases=self.databases)
+
+        msg = f"{expression} cannot be used in db_default."
+        expected_error = Error(msg=msg, obj=field, id="fields.E012")
+        self.assertEqual(errors, [expected_error])
diff --git a/tests/migrations/test_autodetector.py b/tests/migrations/test_autodetector.py
index ee199fea68..74892bbf3d 100644
--- a/tests/migrations/test_autodetector.py
+++ b/tests/migrations/test_autodetector.py
@@ -269,6 +269,14 @@ class AutodetectorTests(BaseAutodetectorTests):
             ("name", models.CharField(max_length=200, default="Ada Lovelace")),
         ],
     )
+    author_name_db_default = ModelState(
+        "testapp",
+        "Author",
+        [
+            ("id", models.AutoField(primary_key=True)),
+            ("name", models.CharField(max_length=200, db_default="Ada Lovelace")),
+        ],
+    )
     author_name_check_constraint = ModelState(
         "testapp",
         "Author",
@@ -1293,6 +1301,21 @@ class AutodetectorTests(BaseAutodetectorTests):
         "django.db.migrations.questioner.MigrationQuestioner.ask_not_null_addition",
         side_effect=AssertionError("Should not have prompted for not null addition"),
     )
+    def test_add_not_null_field_with_db_default(self, mocked_ask_method):
+        changes = self.get_changes([self.author_empty], [self.author_name_db_default])
+        self.assertNumberMigrations(changes, "testapp", 1)
+        self.assertOperationTypes(changes, "testapp", 0, ["AddField"])
+        self.assertOperationAttributes(
+            changes, "testapp", 0, 0, name="name", preserve_default=True
+        )
+        self.assertOperationFieldAttributes(
+            changes, "testapp", 0, 0, db_default=models.Value("Ada Lovelace")
+        )
+
+    @mock.patch(
+        "django.db.migrations.questioner.MigrationQuestioner.ask_not_null_addition",
+        side_effect=AssertionError("Should not have prompted for not null addition"),
+    )
     def test_add_date_fields_with_auto_now_not_asking_for_default(
         self, mocked_ask_method
     ):
@@ -1480,6 +1503,23 @@ class AutodetectorTests(BaseAutodetectorTests):
 
     @mock.patch(
         "django.db.migrations.questioner.MigrationQuestioner.ask_not_null_alteration",
+        side_effect=AssertionError("Should not have prompted for not null alteration"),
+    )
+    def test_alter_field_to_not_null_with_db_default(self, mocked_ask_method):
+        changes = self.get_changes(
+            [self.author_name_null], [self.author_name_db_default]
+        )
+        self.assertNumberMigrations(changes, "testapp", 1)
+        self.assertOperationTypes(changes, "testapp", 0, ["AlterField"])
+        self.assertOperationAttributes(
+            changes, "testapp", 0, 0, name="name", preserve_default=True
+        )
+        self.assertOperationFieldAttributes(
+            changes, "testapp", 0, 0, db_default=models.Value("Ada Lovelace")
+        )
+
+    @mock.patch(
+        "django.db.migrations.questioner.MigrationQuestioner.ask_not_null_alteration",
         return_value=models.NOT_PROVIDED,
     )
     def test_alter_field_to_not_null_without_default(self, mocked_ask_method):
diff --git a/tests/migrations/test_base.py b/tests/migrations/test_base.py
index f038cd7605..b5228ad445 100644
--- a/tests/migrations/test_base.py
+++ b/tests/migrations/test_base.py
@@ -292,6 +292,13 @@ class OperationTestBase(MigrationTestBase):
                     ("id", models.AutoField(primary_key=True)),
                     ("pink", models.IntegerField(default=3)),
                     ("weight", models.FloatField()),
+                    ("green", models.IntegerField(null=True)),
+                    (
+                        "yellow",
+                        models.CharField(
+                            blank=True, null=True, db_default="Yellow", max_length=20
+                        ),
+                    ),
                 ],
                 options=model_options,
             )
diff --git a/tests/migrations/test_operations.py b/tests/migrations/test_operations.py
index b67a871bc8..e377e4ca64 100644
--- a/tests/migrations/test_operations.py
+++ b/tests/migrations/test_operations.py
@@ -1,14 +1,18 @@
+import math
+
 from django.core.exceptions import FieldDoesNotExist
 from django.db import IntegrityError, connection, migrations, models, transaction
 from django.db.migrations.migration import Migration
 from django.db.migrations.operations.fields import FieldOperation
 from django.db.migrations.state import ModelState, ProjectState
-from django.db.models.functions import Abs
+from django.db.models.expressions import Value
+from django.db.models.functions import Abs, Pi
 from django.db.transaction import atomic
 from django.test import (
     SimpleTestCase,
     ignore_warnings,
     override_settings,
+    skipIfDBFeature,
     skipUnlessDBFeature,
 )
 from django.test.utils import CaptureQueriesContext
@@ -1340,7 +1344,7 @@ class OperationTests(OperationTestBase):
         self.assertEqual(operation.describe(), "Add field height to Pony")
         self.assertEqual(operation.migration_name_fragment, "pony_height")
         project_state, new_state = self.make_test_state("test_adfl", operation)
-        self.assertEqual(len(new_state.models["test_adfl", "pony"].fields), 4)
+        self.assertEqual(len(new_state.models["test_adfl", "pony"].fields), 6)
         field = new_state.models["test_adfl", "pony"].fields["height"]
         self.assertEqual(field.default, 5)
         # Test the database alteration
@@ -1528,7 +1532,7 @@ class OperationTests(OperationTestBase):
         )
         new_state = project_state.clone()
         operation.state_forwards("test_adflpd", new_state)
-        self.assertEqual(len(new_state.models["test_adflpd", "pony"].fields), 4)
+        self.assertEqual(len(new_state.models["test_adflpd", "pony"].fields), 6)
         field = new_state.models["test_adflpd", "pony"].fields["height"]
         self.assertEqual(field.default, models.NOT_PROVIDED)
         # Test the database alteration
@@ -1547,6 +1551,169 @@ class OperationTests(OperationTestBase):
             sorted(definition[2]), ["field", "model_name", "name", "preserve_default"]
         )
 
+    def test_add_field_database_default(self):
+        """The AddField operation can set and unset a database default."""
+        app_label = "test_adfldd"
+        table_name = f"{app_label}_pony"
+        project_state = self.set_up_test_model(app_label)
+        operation = migrations.AddField(
+            "Pony", "height", models.FloatField(null=True, db_default=4)
+        )
+        new_state = project_state.clone()
+        operation.state_forwards(app_label, new_state)
+        self.assertEqual(len(new_state.models[app_label, "pony"].fields), 6)
+        field = new_state.models[app_label, "pony"].fields["height"]
+        self.assertEqual(field.default, models.NOT_PROVIDED)
+        self.assertEqual(field.db_default, Value(4))
+        project_state.apps.get_model(app_label, "pony").objects.create(weight=4)
+        self.assertColumnNotExists(table_name, "height")
+        # Add field.
+        with connection.schema_editor() as editor:
+            operation.database_forwards(app_label, editor, project_state, new_state)
+        self.assertColumnExists(table_name, "height")
+        new_model = new_state.apps.get_model(app_label, "pony")
+        old_pony = new_model.objects.get()
+        self.assertEqual(old_pony.height, 4)
+        new_pony = new_model.objects.create(weight=5)
+        if not connection.features.can_return_columns_from_insert:
+            new_pony.refresh_from_db()
+        self.assertEqual(new_pony.height, 4)
+        # Reversal.
+        with connection.schema_editor() as editor:
+            operation.database_backwards(app_label, editor, new_state, project_state)
+        self.assertColumnNotExists(table_name, "height")
+        # Deconstruction.
+        definition = operation.deconstruct()
+        self.assertEqual(definition[0], "AddField")
+        self.assertEqual(definition[1], [])
+        self.assertEqual(
+            definition[2],
+            {
+                "field": field,
+                "model_name": "Pony",
+                "name": "height",
+            },
+        )
+
+    def test_add_field_database_default_special_char_escaping(self):
+        app_label = "test_adflddsce"
+        table_name = f"{app_label}_pony"
+        project_state = self.set_up_test_model(app_label)
+        old_pony_pk = (
+            project_state.apps.get_model(app_label, "pony").objects.create(weight=4).pk
+        )
+        tests = ["%", "'", '"']
+        for db_default in tests:
+            with self.subTest(db_default=db_default):
+                operation = migrations.AddField(
+                    "Pony",
+                    "special_char",
+                    models.CharField(max_length=1, db_default=db_default),
+                )
+                new_state = project_state.clone()
+                operation.state_forwards(app_label, new_state)
+                self.assertEqual(len(new_state.models[app_label, "pony"].fields), 6)
+                field = new_state.models[app_label, "pony"].fields["special_char"]
+                self.assertEqual(field.default, models.NOT_PROVIDED)
+                self.assertEqual(field.db_default, Value(db_default))
+                self.assertColumnNotExists(table_name, "special_char")
+                with connection.schema_editor() as editor:
+                    operation.database_forwards(
+                        app_label, editor, project_state, new_state
+                    )
+                self.assertColumnExists(table_name, "special_char")
+                new_model = new_state.apps.get_model(app_label, "pony")
+                try:
+                    new_pony = new_model.objects.create(weight=5)
+                    if not connection.features.can_return_columns_from_insert:
+                        new_pony.refresh_from_db()
+                    self.assertEqual(new_pony.special_char, db_default)
+
+                    old_pony = new_model.objects.get(pk=old_pony_pk)
+                    if connection.vendor != "oracle" or db_default != "'":
+                        # The single quotation mark ' is properly quoted and is
+                        # set for new rows on Oracle, however it is not set on
+                        # existing rows. Skip the assertion as it's probably a
+                        # bug in Oracle.
+                        self.assertEqual(old_pony.special_char, db_default)
+                finally:
+                    with connection.schema_editor() as editor:
+                        operation.database_backwards(
+                            app_label, editor, new_state, project_state
+                        )
+
+    @skipUnlessDBFeature("supports_expression_defaults")
+    def test_add_field_database_default_function(self):
+        app_label = "test_adflddf"
+        table_name = f"{app_label}_pony"
+        project_state = self.set_up_test_model(app_label)
+        operation = migrations.AddField(
+            "Pony", "height", models.FloatField(db_default=Pi())
+        )
+        new_state = project_state.clone()
+        operation.state_forwards(app_label, new_state)
+        self.assertEqual(len(new_state.models[app_label, "pony"].fields), 6)
+        field = new_state.models[app_label, "pony"].fields["height"]
+        self.assertEqual(field.default, models.NOT_PROVIDED)
+        self.assertEqual(field.db_default, Pi())
+        project_state.apps.get_model(app_label, "pony").objects.create(weight=4)
+        self.assertColumnNotExists(table_name, "height")
+        # Add field.
+        with connection.schema_editor() as editor:
+            operation.database_forwards(app_label, editor, project_state, new_state)
+        self.assertColumnExists(table_name, "height")
+        new_model = new_state.apps.get_model(app_label, "pony")
+        old_pony = new_model.objects.get()
+        self.assertAlmostEqual(old_pony.height, math.pi)
+        new_pony = new_model.objects.create(weight=5)
+        if not connection.features.can_return_columns_from_insert:
+            new_pony.refresh_from_db()
+        self.assertAlmostEqual(old_pony.height, math.pi)
+
+    def test_add_field_both_defaults(self):
+        """The AddField operation with both default and db_default."""
+        app_label = "test_adflbddd"
+        table_name = f"{app_label}_pony"
+        project_state = self.set_up_test_model(app_label)
+        operation = migrations.AddField(
+            "Pony", "height", models.FloatField(default=3, db_default=4)
+        )
+        new_state = project_state.clone()
+        operation.state_forwards(app_label, new_state)
+        self.assertEqual(len(new_state.models[app_label, "pony"].fields), 6)
+        field = new_state.models[app_label, "pony"].fields["height"]
+        self.assertEqual(field.default, 3)
+        self.assertEqual(field.db_default, Value(4))
+        project_state.apps.get_model(app_label, "pony").objects.create(weight=4)
+        self.assertColumnNotExists(table_name, "height")
+        # Add field.
+        with connection.schema_editor() as editor:
+            operation.database_forwards(app_label, editor, project_state, new_state)
+        self.assertColumnExists(table_name, "height")
+        new_model = new_state.apps.get_model(app_label, "pony")
+        old_pony = new_model.objects.get()
+        self.assertEqual(old_pony.height, 4)
+        new_pony = new_model.objects.create(weight=5)
+        if not connection.features.can_return_columns_from_insert:
+            new_pony.refresh_from_db()
+        self.assertEqual(new_pony.height, 3)
+        # Reversal.
+        with connection.schema_editor() as editor:
+            operation.database_backwards(app_label, editor, new_state, project_state)
+        self.assertColumnNotExists(table_name, "height")
+        # Deconstruction.
+        definition = operation.deconstruct()
+        self.assertEqual(definition[0], "AddField")
+        self.assertEqual(definition[1], [])
+        self.assertEqual(
+            definition[2],
+            {
+                "field": field,
+                "model_name": "Pony",
+                "name": "height",
+            },
+        )
+
     def test_add_field_m2m(self):
         """
         Tests the AddField operation with a ManyToManyField.
@@ -1558,7 +1725,7 @@ class OperationTests(OperationTestBase):
         )
         new_state = project_state.clone()
         operation.state_forwards("test_adflmm", new_state)
-        self.assertEqual(len(new_state.models["test_adflmm", "pony"].fields), 4)
+        self.assertEqual(len(new_state.models["test_adflmm", "pony"].fields), 6)
         # Test the database alteration
         self.assertTableNotExists("test_adflmm_pony_stables")
         with connection.schema_editor() as editor:
@@ -1727,7 +1894,7 @@ class OperationTests(OperationTestBase):
         self.assertEqual(operation.migration_name_fragment, "remove_pony_pink")
         new_state = project_state.clone()
         operation.state_forwards("test_rmfl", new_state)
-        self.assertEqual(len(new_state.models["test_rmfl", "pony"].fields), 2)
+        self.assertEqual(len(new_state.models["test_rmfl", "pony"].fields), 4)
         # Test the database alteration
         self.assertColumnExists("test_rmfl_pony", "pink")
         with connection.schema_editor() as editor:
@@ -1934,6 +2101,146 @@ class OperationTests(OperationTestBase):
         self.assertEqual(definition[1], [])
         self.assertEqual(sorted(definition[2]), ["field", "model_name", "name"])
 
+    def test_alter_field_add_database_default(self):
+        app_label = "test_alfladd"
+        project_state = self.set_up_test_model(app_label)
+        operation = migrations.AlterField(
+            "Pony", "weight", models.FloatField(db_default=4.5)
+        )
+        new_state = project_state.clone()
+        operation.state_forwards(app_label, new_state)
+        old_weight = project_state.models[app_label, "pony"].fields["weight"]
+        self.assertIs(old_weight.db_default, models.NOT_PROVIDED)
+        new_weight = new_state.models[app_label, "pony"].fields["weight"]
+        self.assertEqual(new_weight.db_default, Value(4.5))
+        with self.assertRaises(IntegrityError), transaction.atomic():
+            project_state.apps.get_model(app_label, "pony").objects.create()
+        # Alter field.
+        with connection.schema_editor() as editor:
+            operation.database_forwards(app_label, editor, project_state, new_state)
+        pony = new_state.apps.get_model(app_label, "pony").objects.create()
+        if not connection.features.can_return_columns_from_insert:
+            pony.refresh_from_db()
+        self.assertEqual(pony.weight, 4.5)
+        # Reversal.
+        with connection.schema_editor() as editor:
+            operation.database_backwards(app_label, editor, new_state, project_state)
+        with self.assertRaises(IntegrityError), transaction.atomic():
+            project_state.apps.get_model(app_label, "pony").objects.create()
+        # Deconstruction.
+        definition = operation.deconstruct()
+        self.assertEqual(definition[0], "AlterField")
+        self.assertEqual(definition[1], [])
+        self.assertEqual(
+            definition[2],
+            {
+                "field": new_weight,
+                "model_name": "Pony",
+                "name": "weight",
+            },
+        )
+
+    def test_alter_field_change_default_to_database_default(self):
+        """The AlterField operation changing default to db_default."""
+        app_label = "test_alflcdtdd"
+        project_state = self.set_up_test_model(app_label)
+        operation = migrations.AlterField(
+            "Pony", "pink", models.IntegerField(db_default=4)
+        )
+        new_state = project_state.clone()
+        operation.state_forwards(app_label, new_state)
+        old_pink = project_state.models[app_label, "pony"].fields["pink"]
+        self.assertEqual(old_pink.default, 3)
+        self.assertIs(old_pink.db_default, models.NOT_PROVIDED)
+        new_pink = new_state.models[app_label, "pony"].fields["pink"]
+        self.assertIs(new_pink.default, models.NOT_PROVIDED)
+        self.assertEqual(new_pink.db_default, Value(4))
+        pony = project_state.apps.get_model(app_label, "pony").objects.create(weight=1)
+        self.assertEqual(pony.pink, 3)
+        # Alter field.
+        with connection.schema_editor() as editor:
+            operation.database_forwards(app_label, editor, project_state, new_state)
+        pony = new_state.apps.get_model(app_label, "pony").objects.create(weight=1)
+        if not connection.features.can_return_columns_from_insert:
+            pony.refresh_from_db()
+        self.assertEqual(pony.pink, 4)
+        # Reversal.
+        with connection.schema_editor() as editor:
+            operation.database_backwards(app_label, editor, new_state, project_state)
+        pony = project_state.apps.get_model(app_label, "pony").objects.create(weight=1)
+        self.assertEqual(pony.pink, 3)
+
+    def test_alter_field_change_nullable_to_database_default_not_null(self):
+        """
+        The AlterField operation changing a null field to db_default.
+        """
+        app_label = "test_alflcntddnn"
+        project_state = self.set_up_test_model(app_label)
+        operation = migrations.AlterField(
+            "Pony", "green", models.IntegerField(db_default=4)
+        )
+        new_state = project_state.clone()
+        operation.state_forwards(app_label, new_state)
+        old_green = project_state.models[app_label, "pony"].fields["green"]
+        self.assertIs(old_green.db_default, models.NOT_PROVIDED)
+        new_green = new_state.models[app_label, "pony"].fields["green"]
+        self.assertEqual(new_green.db_default, Value(4))
+        old_pony = project_state.apps.get_model(app_label, "pony").objects.create(
+            weight=1
+        )
+        self.assertIsNone(old_pony.green)
+        # Alter field.
+        with connection.schema_editor() as editor:
+            operation.database_forwards(app_label, editor, project_state, new_state)
+        old_pony.refresh_from_db()
+        self.assertEqual(old_pony.green, 4)
+        pony = new_state.apps.get_model(app_label, "pony").objects.create(weight=1)
+        if not connection.features.can_return_columns_from_insert:
+            pony.refresh_from_db()
+        self.assertEqual(pony.green, 4)
+        # Reversal.
+        with connection.schema_editor() as editor:
+            operation.database_backwards(app_label, editor, new_state, project_state)
+        pony = project_state.apps.get_model(app_label, "pony").objects.create(weight=1)
+        self.assertIsNone(pony.green)
+
+    @skipIfDBFeature("interprets_empty_strings_as_nulls")
+    def test_alter_field_change_blank_nullable_database_default_to_not_null(self):
+        app_label = "test_alflcbnddnn"
+        table_name = f"{app_label}_pony"
+        project_state = self.set_up_test_model(app_label)
+        default = "Yellow"
+        operation = migrations.AlterField(
+            "Pony",
+            "yellow",
+            models.CharField(blank=True, db_default=default, max_length=20),
+        )
+        new_state = project_state.clone()
+        operation.state_forwards(app_label, new_state)
+        self.assertColumnNull(table_name, "yellow")
+        pony = project_state.apps.get_model(app_label, "pony").objects.create(
+            weight=1, yellow=None
+        )
+        self.assertIsNone(pony.yellow)
+        # Alter field.
+        with connection.schema_editor() as editor:
+            operation.database_forwards(app_label, editor, project_state, new_state)
+        self.assertColumnNotNull(table_name, "yellow")
+        pony.refresh_from_db()
+        self.assertEqual(pony.yellow, default)
+        pony = new_state.apps.get_model(app_label, "pony").objects.create(weight=1)
+        if not connection.features.can_return_columns_from_insert:
+            pony.refresh_from_db()
+        self.assertEqual(pony.yellow, default)
+        # Reversal.
+        with connection.schema_editor() as editor:
+            operation.database_backwards(app_label, editor, new_state, project_state)
+        self.assertColumnNull(table_name, "yellow")
+        pony = project_state.apps.get_model(app_label, "pony").objects.create(
+            weight=1, yellow=None
+        )
+        self.assertIsNone(pony.yellow)
+
     def test_alter_field_add_db_column_noop(self):
         """
         AlterField operation is a noop when adding only a db_column and the
diff --git a/tests/schema/tests.py b/tests/schema/tests.py
index d81a01b41d..688a9f1fcf 100644
--- a/tests/schema/tests.py
+++ b/tests/schema/tests.py
@@ -2102,6 +2102,33 @@ class SchemaTests(TransactionTestCase):
         with self.assertRaises(IntegrityError):
             NoteRename.objects.create(detail_info=None)
 
+    @isolate_apps("schema")
+    def test_rename_keep_db_default(self):
+        """Renaming a field shouldn't affect a database default."""
+
+        class AuthorDbDefault(Model):
+            birth_year = IntegerField(db_default=1985)
+
+            class Meta:
+                app_label = "schema"
+
+        self.isolated_local_models = [AuthorDbDefault]
+        with connection.schema_editor() as editor:
+            editor.create_model(AuthorDbDefault)
+        columns = self.column_classes(AuthorDbDefault)
+        self.assertEqual(columns["birth_year"][1].default, "1985")
+
+        old_field = AuthorDbDefault._meta.get_field("birth_year")
+        new_field = IntegerField(db_default=1985)
+        new_field.set_attributes_from_name("renamed_year")
+        new_field.model = AuthorDbDefault
+        with connection.schema_editor(
+            atomic=connection.features.supports_atomic_references_rename
+        ) as editor:
+            editor.alter_field(AuthorDbDefault, old_field, new_field, strict=True)
+        columns = self.column_classes(AuthorDbDefault)
+        self.assertEqual(columns["renamed_year"][1].default, "1985")
+
     @skipUnlessDBFeature(
         "supports_column_check_constraints", "can_introspect_check_constraints"
     )