Supported use case for foreign key constraints where the local column is
marked as "invisible". The errors normally generated when a
:class:`.ForeignKeyConstraint` is created that check for the target column
are disabled when reflecting, and the constraint is skipped with a warning
in the same way which already occurs for an :class:`.Index` with a similar
issue.

tests are added for indexes, unique constraints, and primary key
constraints, which were already working; indexes and uniques warn,
primary keys don't which we would assume is because we never see those
PK columns in the first place.

Constraints now raise an informative ConstraintColumnNotFoundError
in the general case for strings in the "pending colargs" collection
not being resolvable.

Fixes: #9059
Change-Id: I400cf0bff6abba0e0c75f38b07617be1a8ec3453

Restored the behavior of :meth:`.Inspector.has_table` to report on
temporary tables for MySQL / MariaDB. This is currently the behavior for
all other included dialects, but was removed for MySQL in 1.4 due to no
longer using the DESCRIBE command; there was no documented support for temp
tables being reported by the :meth:`.Inspector.has_table` method in this
version or on any previous version, so the previous behavior was undefined.

As SQLAlchemy 2.0 has added formal support for temp table status via
:meth:`.Inspector.has_table`, the MySQL /MariaDB dialect has been reverted
to use the "DESCRIBE" statement as it did in the SQLAlchemy 1.3 series and
previously, and test support is added to include MySQL / MariaDB for
this behavior.   The previous issues with ROLLBACK being emitted which
1.4 sought to improve upon don't apply in SQLAlchemy 2.0 due to
simplifications in how :class:`.Connection` handles transactions.

DESCRIBE is necessary as MariaDB in particular has no consistently
available public information schema of any kind in order to report on temp
tables other than DESCRIBE/SHOW COLUMNS, which rely on throwing an error
in order to report no results.

Fixes: #9058
Change-Id: Ic511bd5989ec17beb37b7cddd913732b626af0e6

Change-Id: I625af65b3fb1815b1af17dc2ef47dd697fdc3fb1

command run is "pyupgrade --py37-plus --keep-runtime-typing --keep-percent-format <files...>"
pyupgrade will change assert_ to assertTrue. That was reverted since assertTrue does not
exists in sqlalchemy fixtures

Change-Id: Ie1ed2675c7b11d893d78e028aad0d1576baebb55

Change-Id: I5a241a70efba68bcea9819ddce6aebc25703e68d

The PostgreSQL dialect now supports reflection of expression based indexes.
The reflection is supported both when using
:meth:`_engine.Inspector.get_indexes` and when reflecting a
:class:`_schema.Table` using :paramref:`_schema.Table.autoload_with`.
Thanks to immerrr and Aidan Kane for the help on this ticket.

Fixes: #7442
Change-Id: I3e36d557235286c0f7f6d8276272ff9225058d48

Point to the typed dict for the documentation instead of
duplicating it in the mothod text.

Change-Id: I041abee7dc27b95409950741e702d69101c22c6d

Adds support for comments on named constraints, including `ForeignKeyConstraint`, `PrimaryKeyConstraint`, `CheckConstraint`, `UniqueConstraint`, solving the [Issue 5667](https://github.com/sqlalchemy/sqlalchemy/issues/5667).

Supports only PostgreSQL backend.

### Description

Following the example of [Issue 1546](https://github.com/sqlalchemy/sqlalchemy/issues/1546), supports comments on constraints. Specifically, enables comments on _named_ ones — as I get it, PostgreSQL prohibits comments on unnamed constraints.

Enables setting the comments for named constraints like this:
```
Table(
   'example', metadata,
   Column('id', Integer),
   Column('data', sa.String(30)),
   PrimaryKeyConstraint(
       "id", name="id_pk", comment="id_pk comment"
    ),
   CheckConstraint('id < 100', name="cc1", comment="Id value can't exceed 100"),
   UniqueConstraint(['data'], name="uc1", comment="Must have unique data field"),
)
```

Provides the DDL representation for constraint comments and routines to create and drop them. Class `.Inspector` reflects constraint comments via methods like `get_check_constraints` .
### Checklist
<!-- go over following points. check them with an `x` if they do apply, (they turn into clickable checkboxes once the PR is submitted, so no need to do everything at once)

-->

This pull request is:

- [ ] A documentation / typographical error fix
- [ ] A short code fix
- [x] A new feature implementation
	- Solves the issue 5667.
	- The commit message includes `Fixes: 5667`.
	- Includes tests based on comment reflection.

**Have a nice day!**

Fixes: #5667
Closes: #7742
Pull-request: https://github.com/sqlalchemy/sqlalchemy/pull/7742
Pull-request-sha: 42a5d3c3e9ccf9a9d5397fd007aeab0854f66130

Change-Id: Ia60f578595afdbd6089541c9a00e37997ef78ad3

The warnings that are emitted regarding reflection of indexes or unique
constraints, when the :paramref:`.Table.include_columns` parameter is used
to exclude columns that are then found to be part of those constraints,
have been removed. When the :paramref:`.Table.include_columns` parameter is
used it should be expected that the resulting :class:`.Table` construct
will not include constraints that rely upon omitted columns. This change
was made in response to :ticket:`8100` which repaired
:paramref:`.Table.include_columns` in conjunction with foreign key
constraints that rely upon omitted columns, where the use case became
clear that omitting such constraints should be expected.

Fixes: #8102
Change-Id: Id32f628def2d12499cd49d0b436ed345fe49dc6b