Add support to ``FETCH {FIRST | NEXT} [ count ] {ROW | ROWS}
 {ONLY | WITH TIES}`` in the select for the supported backends,
currently PostgreSQL, Oracle and MSSQL.

Fixes: #5576
Change-Id: Ibb5871a457c0555f82b37e354e7787d15575f1f7

Change-Id: Id9ac0b45f0859199e7db61ef5d4fac956b74b2ba

Added support for reflecting "identity" columns, which are now returned
as part of the structure returned by :meth:`_reflection.Inspector.get_columns`.
When reflecting full :class:`_schema.Table` objects, identity columns will
be represented using the :class:`_schema.Identity` construct.

Fixed compilation error on oracle for sequence and identity column
``nominvalue`` and ``nomaxvalue`` options that require no space in them.

Improved test compatibility with oracle 18.

As part of the support for reflecting :class:`_schema.Identity` objects,
the method :meth:`_reflection.Inspector.get_columns` no longer returns
``mssql_identity_start`` and ``mssql_identity_increment`` as part of the
``dialect_options``. Use the information in the ``identity`` key instead.

The mssql dialect will assume that at least MSSQL 2005 is used.
There is no hard exception raised if a previous version is detected,
but operations may fail for older versions.

Fixes: #5527
Fixes: #5324
Change-Id: If039fe637c46b424499e6bac54a2cbc0dc54cb57

It's better, the majority of these changes look more readable to me.
also found some docstrings that had formatting / quoting issues.

Change-Id: I582a45fde3a5648b2f36bab96bad56881321899b

Set default type codec for ``json`` and ``jsonb`` types when using
the asyncpg driver. By default asyncpg will not decode them and return
strings instead.

Fixes: #5584
Change-Id: I41348eff8096ccf87b952d7e797c0694c6c4b5c4

Provide support for multiple hosts in the PostgreSQL connection string.

A user requested for SQLAlchemy to support multiple hosts within a PostgreSQL URL string. The proposed fix allows this. In the event that the url contains multiple hosts the proposed code will convert the query["hosts"] tuple into a single string. This allows the hosts to then get converted into a valid dsn variable in the psycopg2 connect function.

This pull request is:

- [ ] A documentation / typographical error fix
	- Good to go, no issue or tests are needed
- [X ] A short code fix
	- please include the issue number, and create an issue if none exists, which
	  must include a complete example of the issue.  one line code fixes without an
	  issue and demonstration will not be accepted.
	- Please include: `Fixes: #<issue number>` in the commit message
	- please include tests.   one line code fixes without tests will not be accepted.
- [ ] A new feature implementation
	- please include the issue number, and create an issue if none exists, which must
	  include a complete example of how the feature would look.
	- Please include: `Fixes: #<issue number>` in the commit message
	- please include tests.

**Have a nice day!**
Fixes: #4392

Closes: #5554
Pull-request: https://github.com/sqlalchemy/sqlalchemy/pull/5554
Pull-request-sha: 3f7a0ab8df9f1411a9f1ac0e152583bc7bf0c365

Change-Id: I3f3768d51b8331de786ffdc025b7ecfc662eafe5

This codec was used to ensure the "pg_attribute.generated"
column comes back as a string and not bytes, matching how
other PG drivers treat this datatype.   However, this breaks
asyncpg's internal implementation of set_type_codec going forward
and the "char" datatype is actually a bytes in any case.
So at the moment it appears psycopg2/pg8000 are broken for mis-treatment
of the datatype and asyncpg is broken in that it was allowing
us to change a codec that it appears to rely upon internally.

Fixes: #5586
Change-Id: I937eba315904721aa4e2726b95432910a8affe5f

The server_side_cursors engine-wide feature relies upon
regexp parsing of statements a well as general guessing as
to when the feature should be used.   This is not within the
2.0 way of doing things and should be removed.

Additionally, mariadbconnector defaults to unbuffered cursors;
add new cursor hooks so that mariadbconnector can specify
buffered or unbuffered cursors without too much difficulty.
This will also correctly default mariadbconnector to buffered
cursors which should repair the segfaults we've been getting.

Try to restore the assert_raises that was removed in
5b6dfc0c38bf1f01da4b8 to see if mariadbconnector segfaults
are resolved.

Change-Id: I77f1c972c742e40694972f578140bb0cac8c39eb