Fixed bug where an UPDATE statement against a JOIN using MySQL multi-table
format would fail to include the table prefix for the target table if the
statement had no WHERE clause, as only the WHERE clause were scanned to
detect a "multi table update" at that particular point.  The target
is now also scanned if it's a JOIN to get the leftmost table as the
primary table and the additional entries as additional FROM entries.

Fixes: #5617
Change-Id: I26d74afebe06e28af28acf960258f170a1627823

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

As the test suite has widespread use of many patterns
that are deprecated, enable SQLALCHEMY_WARN_20 globally
for the test suite but then break the warnings filter
out into a whole list of all the individual warnings
we are looking for.  this way individual changesets
can target a specific class of warning, as many of these
warnings will indivdidually affect dozens of files
and potentially hundreds of lines of code.

Many warnings are also resolved here as this
patch started out that way.   From this point
forward there should be changesets that target a
subset of the warnings at a time.

For expediency, updates some migration 2.0 docs
for ORM as well.

Change-Id: I98b8defdf7c37b818b3824d02f7668e3f5f31c94

This change includes mainly that the bracketed use within
select() is moved to positional, and keyword arguments are
removed from calls to the select() function.  it does not
yet fully address other issues such as keyword arguments passed
to the table.select().

Additionally, allows False / None to both be considered
as "disable" for all of select.correlate(), select.correlate_except(),
query.correlate(), which establishes consistency with
passing of ``False`` for the legact select(correlate=False)
argument.

Change-Id: Ie6c6e6abfbd3d75d4c8de504c0cf0159e6999108

The fix in 180ae7c1a53385f72b0047496ac001ec5099cc3e
didn't do much as the code was not preserving parameter
order at all, in fact.    Reworked stmt_parameters to be
delivered in the correct order up front and preserve
throughout crud.py which was not being done at all
before.

Fixes: #5510
Change-Id: I0795c71df73005a25d1bbf216732d41b41e11a5f

The test for the parameter fix in c0685e5f41 was not working
deterministically on Python 2, so use ordered_values(), however
a second issue in ordered_values() was assuming each element was a
column, so also test for array-assignment expressions with
ordered_values.

Change-Id: I944c72a52700ffb4ab5ae1a83ae21f1efc84b505

Fixes related to rendering of complex UPDATE DML
which was not correctly preserving positional parameter
order in conjunction with DML features that are only known
to work on the PostgreSQL database.    Both pg8000
and asyncpg use positional parameters which is why these
issues are suddenly apparent.

crud.py now takes on the task of rendering the column
expressions for SET or VALUES so that for the very unusual
case that the column expression is a compound expression
that includes a bound parameter (namely an array index),
the bound parameter order is preserved.

Additionally, crud.py passes through the positional_names
keyword argument into bindparam_string() which is necessary
when CTEs are being rendered, as PG supports complex
CTE / INSERT / UPDATE scenarios.

Change-Id: I7f03920500e19b721636b84594de78a5bfdcbc82

The psycopg2 dialect now defaults to using the very performant
``execute_values()`` psycopg2 extension for compiled INSERT statements,
and also impements RETURNING support when this extension is used.  This
allows INSERT statements that even include an autoincremented SERIAL
or IDENTITY value to run very fast while still being able to return the
newly generated primary key values.   The ORM will then integrate this
new feature in a separate change.

Implements RETURNING for insert with executemany

Adds support to return_defaults() mode and inserted_primary_key
to support mutiple INSERTed rows, via return_defauls_rows
and inserted_primary_key_rows accessors.

within default execution context, new cached compiler
getters are used to fetch primary keys from rows

inserted_primary_key now returns a plain tuple. this
is not yet a row-like object however this can be
added.

Adds distinct "values_only" and "batch" modes, as
"values" has a lot of benefits but "batch" breaks
cursor.rowcount

psycopg2 minimum version 2.7 so we can remove the
large number of checks for very old versions of
psycopg2

simplify tests to no longer distinguish between
native and non-native json

Fixes: #5401
Change-Id: Ic08fd3423d4c5d16ca50994460c0c234868bd61c

A variety of caching issues found by running
all tests with statement caching turned on.

The cache system now has a more conservative approach where
any subclass of a SQL element will by default invalidate
the cache key unless it adds the flag inherit_cache=True
at the class level, or if it implements its own caching.

Add working caching to a few elements that were
omitted previously; fix some caching implementations
to suit lesser used edge cases such as json casts
and array slices.

Refine the way BaseCursorResult and CursorMetaData
interact with caching; to suit cases like Alembic
modifying table structures, don't cache the
cursor metadata if it were created against a
cursor.description using non-positional matching,
e.g. "select *".   if a table re-ordered its columns
or added/removed, now that data is obsolete.

Additionally we have to adapt the cursor metadata
_keymap regardless of if we just processed
cursor.description, because if we ran against
a cached SQLCompiler we won't have the right
columns in _keymap.

Other refinements to how and when we do this
adaption as some weird cases
were exposed in the Postgresql dialect,
a text() construct that names just one column that
is not actually in the statement.   Fixed that
also as it looks like a cut-and-paste artifact
that doesn't actually affect anything.

Various issues with re-use of compiled result maps
and cursor metadata in conjunction with tables being
changed, such as change in order of columns.

mappers can be cleared but the class remains, meaning
a mapper has to use itself as the cache key not the class.

lots of bound parameter / literal issues, due to Alembic
creating a straight subclass of bindparam that renders
inline directly.   While we can update Alembic to not
do this, we have to assume other people might be doing
this, so bindparam() implements the inherit_cache=True
logic as well that was a bit involved.

turn on cache stats in logging.

Includes a fix to subqueryloader which moves all setup to
the create_row_processor() phase and elminates any storage
within the compiled context.   This includes some changes
to create_row_processor() signature and a revising of the
technique used to determine if the loader can participate
in polymorphic queries, which is also applied to
selectinloading.

DML update.values() and ordered_values() now coerces the
keys as we have tests that pass an arbitrary class here
which only includes __clause_element__(), so the
key can't be cached unless it is coerced.  this in turn
changed how composite attributes support bulk update
to use the standard approach of ClauseElement with
annotations that are parsed in the ORM context.

memory profiling successfully caught that the Session
from Query was getting passed into _statement_20()
so that was a big win for that test suite.

Apparently Compiler had .execute() and .scalar() methods
stuck on it, these date back to version 0.4 and there
was a single test in the PostgreSQL dialect tests
that exercised it for no apparent reason.   Removed
these methods as well as the concept of a Compiler
holding onto a "bind".

Fixes: #5386

Change-Id: I990b43aab96b42665af1b2187ad6020bee778784

Targeting select / insert / update / delete, the goal
is to minimize overhead of construction and generative methods
so that only the raw arguments passed are handled.   An interim
stage that converts the raw state into more compiler-ready state
is added, which is analogous to the ORM QueryContext which will
also be rolled in to be a similar concept, as is currently
being prototyped in I19e05b3424b07114cce6c439b05198ac47f7ac10.
the ORM update/delete BulkUD concept is also going to be rolled
onto this idea.   So while the compiler-ready state object,
here called DMLState, looks a little thin, it's the
base of a bigger pattern that will allow for ORM functionality
to embed itself directly into the compiler, execution
context, and result set objects.

This change targets the DML objects, primarily focused on the
values() method which is the most complex process.   The
work done by values() is minimized as much as possible
while still being able to create a cache key.   Additional
computation is then offloaded to a new object ValuesState
that is handled by the compiler.

Architecturally, a big change here is that insert.values()
and update.values() will generate BindParameter objects for
the values now, which are then carefully received by crud.py
so that they generate the expected names.   This is so that
the values() portion of these constructs is cacheable.
for the "multi-values" version of Insert, this is all skipped
and the plan right now is that a multi-values insert is
not worth caching (can always be revisited).

Using the
coercions system in values() also gets us nicer validation
for free, we can remove the NotAClauseElement thing from
schema, and we also now require scalar_subquery() is called
for an insert/update that uses a SELECT as a column value,
1.x deprecation path is added.

The traversal system is then applied to the DML objects
including tests so that they have traversal, cloning, and
cache key support.  cloning is not a use case for DML however
having it present allows better validation of the structure
within the tests.

Special per-dialect DML is explicitly not cacheable at the moment,
more as a proof of concept that third party DML constructs can
exist as gracefully not-cacheable rather than producing an
incomplete cache key.

A few selected performance improvements have been added as well,
simplifying the immutabledict.union() method and adding
a new SQLCompiler function that can generate delimeter-separated
clauses like WHERE and ORDER BY without having to build
a ClauseList object at all.   The use of ClauseList will
be removed from Select in an upcoming commit.  Overall,
ClaustList is unnecessary for internal use and only adds
overhead to statement construction and will likely be removed
as much as possible except for explcit use of conjunctions like
and_() and or_().

Change-Id: I408e0b8be91fddd77cf279da97f55020871f75a9