add error code 1049 for mysql has_table

Fixed regression caused by issue :ticket:`9058` which adjusted the MySQL
dialect's ``has_table()`` to again use "DESCRIBE", where the specific error
code raised by MySQL version 8 when using a non-existent schema name was
unexpected and failed to be interpreted as a boolean result.

Fixed the SQLite dialect's ``has_table()`` function to correctly report
False for queries that include a non-None schema name for a schema that
doesn't exist; previously, a database error was raised.

Fixes: #9251
Change-Id: I5ef9cf0887865c3c521d88bca0ba18954a108241

2 files changed, 20 insertions, 1 deletions

diff --git a/lib/sqlalchemy/dialects/mysql/base.py b/lib/sqlalchemy/dialects/mysql/base.py
index 50e0ec07e..3e3578df9 100644
--- a/lib/sqlalchemy/dialects/mysql/base.py
+++ b/lib/sqlalchemy/dialects/mysql/base.py
@@ -2690,7 +2690,21 @@ class MySQLDialect(default.DefaultDialect):
             ) as rs:
                 return rs.fetchone() is not None
         except exc.DBAPIError as e:
-            if self._extract_error_code(e.orig) == 1146:
+            # https://dev.mysql.com/doc/mysql-errors/8.0/en/server-error-reference.html  # noqa: E501
+            # there are a lot of codes that *may* pop up here at some point
+            # but we continue to be fairly conservative.  We include:
+            # 1146: Table '%s.%s' doesn't exist - what every MySQL has emitted
+            # for decades
+            #
+            # mysql 8 suddenly started emitting:
+            # 1049: Unknown database '%s'  - for nonexistent schema
+            #
+            # also added:
+            # 1051: Unknown table '%s' - not known to emit
+            #
+            # there's more "doesn't exist" kinds of messages but they are
+            # less clear if mysql 8 would suddenly start using one of those
+            if self._extract_error_code(e.orig) in (1146, 1049, 1051):
                 return False
             raise
 
diff --git a/lib/sqlalchemy/dialects/sqlite/base.py b/lib/sqlalchemy/dialects/sqlite/base.py
index e46443a74..fcabf5bb8 100644
--- a/lib/sqlalchemy/dialects/sqlite/base.py
+++ b/lib/sqlalchemy/dialects/sqlite/base.py
@@ -2152,6 +2152,11 @@ class SQLiteDialect(default.DefaultDialect):
     def has_table(self, connection, table_name, schema=None, **kw):
         self._ensure_has_table_connection(connection)
 
+        if schema is not None and schema not in self.get_schema_names(
+            connection, **kw
+        ):
+            return False
+
         info = self._get_table_pragma(
             connection, "table_info", table_name, schema=schema
         )