Since the original implementation of CTEs only allowed them in SELECT
queries, the rule rewriter did not expect to find any CTEs in statements
being rewritten by ON INSERT/UPDATE/DELETE rules.  We had dealt with this
to some extent but the code was still several bricks shy of a load, as
illustrated in bug #6051 from Jehan-Guillaume de Rorthais.

In particular, we have to be able to copy CTEs from the original query's
cteList into that of a rule action, in case the rule action references the
CTE (which it pretty much always will).  This also implies we were doing
things in the wrong order in RewriteQuery: we have to recursively rewrite
the CTE queries before expanding the main query, so that we have the
rewritten queries available to copy.

There are unpleasant limitations yet to resolve here, but at least we now
throw understandable FEATURE_NOT_SUPPORTED errors for them instead of just
failing with bizarre implementation-dependent errors.  In particular, we
can't handle propagating the same CTE into multiple post-rewrite queries
(because then the CTE would be evaluated multiple times), and we can't cope
with conflicts between CTE names in the original query and in the rule
actions.

In nearly all cases, the caller already knows the correct collation, and
in a number of places, the value the caller has handy is more correct than
the default for the type would be.  (In particular, this patch makes it
significantly less likely that eval_const_expressions will result in
changing the exposed collation of an expression.)  So an internal lookup
is both expensive and wrong.

This patch implements data-modifying WITH queries according to the
semantics that the updates all happen with the same command counter value,
and in an unspecified order.  Therefore one WITH clause can't see the
effects of another, nor can the outer query see the effects other than
through the RETURNING values.  And attempts to do conflicting updates will
have unpredictable results.  We'll need to document all that.

This commit just fixes the code; documentation updates are waiting on
author.

Marko Tiikkaja and Hitoshi Harada

The recent additions for FDW support required checking foreign-table-ness
in several places in the parse/plan chain.  While it's not clear whether
that would really result in a noticeable slowdown, it seems best to avoid
any performance risk by keeping a copy of the relation's relkind in
RangeTblEntry.  That might have some other uses later, anyway.
Per discussion.

This commit provides the core code and documentation needed.  A contrib
module test case will follow shortly.

Shigeru Hanada, Jan Urbanski, Heikki Linnakangas

This adds collation support for columns and domains, a COLLATE clause
to override it per expression, and B-tree index support.

Peter Eisentraut
reviewed by Pavel Stehule, Itagaki Takahiro, Robert Haas, Noah Misch

A couple of places in the planner need to generate whole-row Vars, and were
cutting corners by setting vartype = RECORDOID in the Vars, even in cases
where there's an identifiable named composite type for the RTE being
referenced.  While we mostly got away with this, it failed when there was
also a parser-generated whole-row reference to the same RTE, because the
two Vars weren't equal() due to the difference in vartype.  Fix by
providing a subroutine the planner can call to generate whole-row Vars
the same way the parser does.

Per bug #5716 from Andrew Tipton.  Back-patch to 9.0 where one of the bogus
calls was introduced (the other one is new in HEAD).

This patch adds the SQL-standard concept of an INSTEAD OF trigger, which
is fired instead of performing a physical insert/update/delete.  The
trigger function is passed the entire old and/or new rows of the view,
and must figure out what to do to the underlying tables to implement
the update.  So this feature can be used to implement updatable views
using trigger programming style rather than rule hacking.

In passing, this patch corrects the names of some columns in the
information_schema.triggers view.  It seems the SQL committee renamed
them somewhere between SQL:99 and SQL:2003.

Dean Rasheed, reviewed by Bernd Helmle; some additional hacking by me.

it works just as well to have them be ordinary identifiers, and this gets rid
of a number of ugly special cases.  Plus we aren't interfering with non-rule
usage of these names.

catversion bump because the names change internally in stored rules.

when FOR UPDATE is propagated down into a sub-select expanded from a view.
Similar bug to parser's isLockedRel issue that I fixed yesterday; likewise
seems not quite worth the effort to back-patch.

underneath the Limit node, not atop it.  This fixes the old problem that such
a query might unexpectedly return fewer rows than the LIMIT says, due to
LockRows discarding updated rows.

There is a related problem that LockRows might destroy the sort ordering
produced by earlier steps; but fixing that by pushing LockRows below Sort
would create serious performance problems that are unjustified in many
real-world applications, as well as potential deadlock problems from locking
many more rows than expected.  Instead, keep the present semantics of applying
FOR UPDATE after ORDER BY within a single query level; but allow the user to
specify the other way by writing FOR UPDATE in a sub-select.  To make that
work, track whether FOR UPDATE appeared explicitly in sub-selects or got
pushed down from the parent, and don't flatten a sub-select that contained an
explicit FOR UPDATE.

for example in
  WITH w AS (SELECT * FROM foo) SELECT * FROM w, bar ... FOR UPDATE
the FOR UPDATE will now affect bar but not foo.  This is more useful and
consistent than the original 8.4 behavior, which tried to propagate FOR UPDATE
into the WITH query but always failed due to assorted implementation
restrictions.  Even though we are in process of removing those restrictions,
it seems correct on philosophical grounds to not let the outer query's
FOR UPDATE affect the WITH query.

In passing, fix isLockedRel which frequently got things wrong in
nested-subquery cases: "FOR UPDATE OF foo" applies to an alias foo in the
current query level, not subqueries.  This has been broken for a long time,
but it doesn't seem worth back-patching further than 8.4 because the actual
consequences are minimal.  At worst the parser would sometimes get
RowShareLock on a relation when it should be AccessShareLock or vice versa.
That would only make a difference if someone were using ExclusiveLock
concurrently, which no standard operation does, and anyway FOR UPDATE
doesn't result in visible changes so it's not clear that the someone would
notice any problem.  Between that and the fact that FOR UPDATE barely works
with subqueries at all in existing releases, I'm not excited about worrying
about it.

a lot of strange behaviors that occurred in join cases.  We now identify the
"current" row for every joined relation in UPDATE, DELETE, and SELECT FOR
UPDATE/SHARE queries.  If an EvalPlanQual recheck is necessary, we jam the
appropriate row into each scan node in the rechecking plan, forcing it to emit
only that one row.  The former behavior could rescan the whole of each joined
relation for each recheck, which was terrible for performance, and what's much
worse could result in duplicated output tuples.

Also, the original implementation of EvalPlanQual could not re-use the recheck
execution tree --- it had to go through a full executor init and shutdown for
every row to be tested.  To avoid this overhead, I've associated a special
runtime Param with each LockRows or ModifyTable plan node, and arranged to
make every scan node below such a node depend on that Param.  Thus, by
signaling a change in that Param, the EPQ machinery can just rescan the
already-built test plan.

This patch also adds a prohibition on set-returning functions in the
targetlist of SELECT FOR UPDATE/SHARE.  This is needed to avoid the
duplicate-output-tuple problem.  It seems fairly reasonable since the
other restrictions on SELECT FOR UPDATE are meant to ensure that there
is a unique correspondence between source tuples and result tuples,
which an output SRF destroys as much as anything else does.

that's generated for a whole-row Var referencing the subquery, when the
subquery is in the nullable side of an outer join.  The previous coding
instead put PlaceHolderVars around the elements of the RowExpr.  The effect
was that when the outer join made the subquery outputs go to null, the
whole-row Var produced ROW(NULL,NULL,...) rather than just NULL.  There
are arguments afoot about whether those things ought to be semantically
indistinguishable, but for the moment they are not entirely so, and the
planner needs to take care that its machinations preserve the difference.
Per bug #5025.

Making this feasible required refactoring ResolveNew() to allow more caller
control over what is substituted for a Var.  I chose to make ResolveNew()
a wrapper around a new general-purpose function replace_rte_variables().
I also fixed the ancient bogosity that ResolveNew might fail to set
a query's hasSubLinks field after inserting a SubLink in it.  Although
all current callers make sure that happens anyway, we've had bugs of that
sort before, and it seemed like a good time to install a proper solution.

Back-patch to 8.4.  The problem can be demonstrated clear back to 8.0,
but the fix would be too invasive in earlier branches; not to mention
that people may be depending on the subtly-incorrect behavior.  The
8.4 series is new enough that fixing this probably won't cause complaints,
but it might in older branches.  Also, 8.4 shows the incorrect behavior
in more cases than older branches do, because it is able to flatten
subqueries in more cases.

provided by Andrew.

Stephen Frost, with help from KaiGai Kohei and others

Bernd Helmle

There are some unimplemented aspects: recursive queries must use UNION ALL
(should allow UNION too), and we don't have SEARCH or CYCLE clauses.
These might or might not get done for 8.4, but even without them it's a
pretty useful feature.

There are also a couple of small loose ends and definitional quibbles,
which I'll send a memo about to pgsql-hackers shortly.  But let's land
the patch now so we can get on with other development.

Yoshiyuki Asaba, with lots of help from Tatsuo Ishii and Tom Lane

a SubLink expression into a rule query.  We missed cases where the original
query contained a sub-SELECT in a function in FROM, a multi-row VALUES list,
or a RETURNING list.  Per bug #4434 from Dean Rasheed and subsequent
investigation.

Back-patch to 8.1; older releases don't have the issue because they didn't
try to be smart about setting hasSubLinks only when needed.

most node types used in expression trees (both before and after parse
analysis).  This allows us to place an error cursor in many situations
where we formerly could not, because the information wasn't available
beyond the very first level of parse analysis.  There's a fair amount
of work still to be done to persuade individual ereport() calls to actually
include an error location, but this gets the initdb-forcing part of the
work out of the way; and the situation is already markedly better than
before for complaints about unimplementable implicit casts, such as
CASE and UNION constructs with incompatible alternative data types.
Per my proposal of a few days ago.

into nodes/nodeFuncs, so as to reduce wanton cross-subsystem #includes inside
the backend.  There's probably more that should be done along this line,
but this is a start anyway.

same line;  previous fix was only partial.  Re-run pgindent on files
that need it.

null::char(3) to a simple Const node.  (It already worked for non-null values,
but not when we skipped evaluation of a strict coercion function.)  This
prevents loss of typmod knowledge in situations such as exhibited in bug
#3598.  Unfortunately there seems no good way to fix that bug in 8.1 and 8.2,
because they simply don't carry a typmod for a plain Const node.

In passing I made all the other callers of makeNullConst supply "real" typmod
values too, though I think it probably doesn't matter anywhere else.

rules to be defined with different, per session controllable, behaviors
for replication purposes.

This will allow replication systems like Slony-I and, as has been stated
on pgsql-hackers, other products to control the firing mechanism of
triggers and rewrite rules without modifying the system catalog directly.

The firing mechanisms are controlled by a new superuser-only GUC
variable, session_replication_role, together with a change to
pg_trigger.tgenabled and a new column pg_rewrite.ev_enabled. Both
columns are a single char data type now (tgenabled was a bool before).
The possible values in these attributes are:

     'O' - Trigger/Rule fires when session_replication_role is "origin"
           (default) or "local". This is the default behavior.

     'D' - Trigger/Rule is disabled and fires never

     'A' - Trigger/Rule fires always regardless of the setting of
           session_replication_role

     'R' - Trigger/Rule fires when session_replication_role is "replica"

The GUC variable can only be changed as long as the system does not have
any cached query plans. This will prevent changing the session role and
accidentally executing stored procedures or functions that have plans
cached that expand to the wrong query set due to differences in the rule
firing semantics.

The SQL syntax for changing a triggers/rules firing semantics is

     ALTER TABLE <tabname> <when> TRIGGER|RULE <name>;

     <when> ::= ENABLE | ENABLE ALWAYS | ENABLE REPLICA | DISABLE

psql's \d command as well as pg_dump are extended in a backward
compatible fashion.

Jan

available information about the typmod of an expression; namely, Const,
ArrayRef, ArrayExpr, and EXPR and ARRAY SubLinks.  In the ArrayExpr and
SubLink cases it wasn't really the data structure's fault, but exprTypmod()
being lazy.  This seems like a good idea in view of the expected increase in
typmod usage from Teodor's work to allow user-defined types to have typmods.
In particular this responds to the concerns we had about eliminating the
special-purpose hack that exprTypmod() used to have for BPCHAR Consts.
We can now tell whether or not such a Const has been cast to a specific
length, and report or display properly if so.

initdb forced due to changes in stored rules.

It has been wrong for this case since it was first written for 7.1 :-(
Per report from Pavel Hanák.

Standard English uses "may", "can", and "might" in different ways:

        may - permission, "You may borrow my rake."

        can - ability, "I can lift that log."

        might - possibility, "It might rain today."

Unfortunately, in conversational English, their use is often mixed, as
in, "You may use this variable to do X", when in fact, "can" is a better
choice.  Similarly, "It may crash" is better stated, "It might crash".

back-stamped for this.

RETURNING play nice with views/rules.  To wit, have the rule rewriter
rewrite any RETURNING clause found in a rule to produce what the rule's
triggering query asked for in its RETURNING clause, in particular drop
the RETURNING clause if no RETURNING in the triggering query.  This
leaves the responsibility for knowing how to produce the view's output
columns on the rule author, without requiring any fundamental changes
in rule semantics such as adding new rule event types would do.  The
initial implementation constrains things to ensure that there is
exactly one, unconditionally invoked RETURNING clause among the rules
for an event --- later we might be able to relax that, but for a post
feature freeze fix it seems better to minimize how much invention we do.
Per gripe from Jaime Casanova.