This adds the very small plugin flake8-import-single which
will prevent us from having an import with more than one symbol
on a line.

Flake8 by itself prevents this pattern with E401:

import collections, os, sys

However does not do anything with this:

from sqlalchemy import Column, text

Both statements have the same issues generating merge artifacts
as well as presenting a manual decision to be made.   While
zimports generally cleans up such imports at the top level, we
don't enforce zimports / pre-commit use.

the plugin finds the same issue for imports that are inside of
test methods.   We shouldn't usually have imports in test methods
so most of them here are moved to be top level.

The version is pinned at 0.1.5; the project seems to have no
activity since 2019, however there are three 0.1.6dev releases
on pypi which stopped in September 2019, they seem to be
experiments with packaging.  The source for 0.1.5
is extremely simple and only reveals one method to flake8
(the run() method).

Change-Id: Icea894e43bad9c0b5d4feb5f49c6c666d6ea6aa1

Fixed bug / regression where using :func:`.bindparam()` with the same name
as a column in the :meth:`.Update.values` method of :class:`.Update`, as
well as the :meth:`.Insert.values` method of :class:`.Insert` in 2.0 only,
would in some cases silently fail to honor the SQL expression in which the
parameter were presented, replacing the expression with a new parameter of
the same name and discarding any other elements of the SQL expression, such
as SQL functions, etc. The specific case would be statements that were
constructed against ORM entities rather than plain :class:`.Table`
instances, but would occur if the statement were invoked with a
:class:`.Session` or a :class:`.Connection`.

:class:`.Update` part of the issue was present in both 2.0 and 1.4 and is
backported to 1.4.

Fixes: #9075
Change-Id: Ie954bc1f492ec6a566163588182ef4910c7ee452

To accommodate for third party dialects with different character escaping
needs regarding bound parameters, the system by which SQLAlchemy "escapes"
(i.e., replaces with another character in its place) special characters in
bound parameter names has been made extensible for third party dialects,
using the :attr:`.SQLCompiler.bindname_escape_chars` dictionary which can
be overridden at the class declaration level on any :class:`.SQLCompiler`
subclass. As part of this change, also added the dot ``"."`` as a default
"escaped" character.

Fixes: #8994
Change-Id: I52fbbfa8c64497b123f57327113df3f022bd1419

The :meth:`.SQLCompiler.construct_params` method, as well as the
:attr:`.SQLCompiler.params` accessor, will now return the
exact parameters that correspond to a compiled statement that used
the ``render_postcompile`` parameter to compile.   Previously,
the method returned a parameter structure that by itself didn't correspond
to either the original parameters or the expanded ones.

Passing a new dictionary of parameters to
:meth:`.SQLCompiler.construct_params` for a :class:`.SQLCompiler` that was
constructed with ``render_postcompile`` is now disallowed; instead, to make
a new SQL string and parameter set for an alternate set of parameters, a
new method :meth:`.SQLCompiler.construct_expanded_state` is added which
will produce a new expanded form for the given parameter set, using the
:class:`.ExpandedState` container which includes a new SQL statement
and new parameter dictionary, as well as a positional parameter tuple.

Fixes: #6114
Change-Id: I9874905bb90f86799b82b244d57369558b18fd93

Changed how the positional compilation is performed. It's rendered by the compiler
the same as the pyformat compilation. The string is then processed to replace
the placeholders with the correct ones, and to obtain the correct order of the
parameters.
This vastly simplifies the computation of the order of the parameters, that in
case of nested CTE is very hard to compute correctly.

Reworked how numeric paramstyle behavers:
- added support for repeated parameter, without duplicating them like in normal
positional dialects
- implement insertmany support. This requires that the dialect supports out of
order placehoders, since all parameters that are not part of the VALUES clauses
are placed at the beginning of the parameter tuple
- support for different identifiers for a numeric parameter. It's for example
possible to use postgresql style placeholder $1, $2, etc

Added two new dialect based on sqlite to test "numeric" fully using
both :1 style and $1 style. Includes a workaround for SQLite's
not-really-correct numeric implementation.

Changed parmstyle of asyncpg dialect to use numeric, rendering with its native
$ identifiers

Fixes: #8926
Fixes: #8849
Change-Id: I7c640467d49adfe6d795cc84296fc7403dcad4d6

Fixed a series of issues regarding positionally rendered bound parameters,
such as those used for SQLite, asyncpg, MySQL and others. Some compiled
forms would not maintain the order of parameters correctly, such as the
PostgreSQL ``regexp_replace()`` function as well as within the "nesting"
feature of the :class:`.CTE` construct first introduced in :ticket:`4123`.

Fixes: #8827
Change-Id: I9813ed7c358cc5c1e26725c48df546b209a442cb

Added :class:`_expression.ScalarValues` that can be used as a column
element allowing using :class:`_expression.Values` inside IN clauses
or in conjunction with ``ANY`` or ``ALL`` collection aggregates.
This new class is generated using the method
:meth:`_expression.Values.scalar_values`.
The :class:`_expression.Values` instance is now coerced to a
:class:`_expression.ScalarValues` when used in a ``IN`` or ``NOT IN``
operation.

Fixes: #6289
Change-Id: Iac22487ccb01553684b908e54d01c0687fa739f1

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

An informative re-raise is now thrown in the case where any "literal
bindparam" render operation fails, indicating the value itself and
the datatype in use, to assist in debugging when literal params
are being rendered in a statement.

Fixes: #8800
Change-Id: Id658f8b03359312353ddbb0c7563026239579f7b

The :class:`.Sequence` construct restores itself to the DDL behavior it
had prior to the 1.4 series, where creating a :class:`.Sequence` with
no additional arguments will emit a simple ``CREATE SEQUENCE`` instruction
**without** any additional parameters for "start value".   For most backends,
this is how things worked previously in any case; **however**, for
MS SQL Server, the default value on this database is
``-2**63``; to prevent this generally impractical default
from taking effect on SQL Server, the :paramref:`.Sequence.start` parameter
should be provided.   As usage of :class:`.Sequence` is unusual
for SQL Server which for many years has standardized on ``IDENTITY``,
it is hoped that this change has minimal impact.

Fixes: #7211
Change-Id: I1207ea10c8cb1528a1519a0fb3581d9621c27b31