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Reduce "Var IS [NOT] NULL" quals during constant folding

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In commit b262ad440, we introduced an optimization that reduces an IS
[NOT] NULL qual on a NOT NULL column to constant true or constant
false, provided we can prove that the input expression of the NullTest
is not nullable by any outer joins or grouping sets.  This deduction
happens quite late in the planner, during the distribution of quals to
rels in query_planner.  However, this approach has some drawbacks: we
can't perform any further folding with the constant, and it turns out
to be prone to bugs.

Ideally, this deduction should happen during constant folding.
However, the per-relation information about which columns are defined
as NOT NULL is not available at that point.  This information is
currently collected from catalogs when building RelOptInfos for base
or "other" relations.

This patch moves the collection of NOT NULL attribute information for
relations before pull_up_sublinks, storing it in a hash table keyed by
relation OID.  It then uses this information to perform the NullTest
deduction for Vars during constant folding.  This also makes it
possible to leverage this information to pull up NOT IN subqueries.

Note that this patch does not get rid of restriction_is_always_true
and restriction_is_always_false.  Removing them would prevent us from
reducing some IS [NOT] NULL quals that we were previously able to
reduce, because (a) the self-join elimination may introduce new IS NOT
NULL quals after constant folding, and (b) if some outer joins are
converted to inner joins, previously irreducible NullTest quals may
become reducible.

Author: Richard Guo <guofenglinux@gmail.com>
Reviewed-by: Robert Haas <robertmhaas@gmail.com>
Reviewed-by: Tom Lane <tgl@sss.pgh.pa.us>
Discussion: https://postgr.es/m/CAMbWs4-bFJ1At4btk5wqbezdu8PLtQ3zv-aiaY3ry9Ymm=jgFQ@mail.gmail.com
This commit is contained in:
Richard Guo
2025-07-22 11:21:36 +09:00
parent 904f6a593a
commit e2debb6438
17 changed files with 336 additions and 81 deletions
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2
contrib/postgres_fdw/sql/postgres_fdw.sql
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@ -352,7 +352,7 @@ EXPLAIN (VERBOSE, COSTS OFF) SELECT * FROM ft1 t1 WHERE c3 IS NULL; -- Nu
EXPLAIN (VERBOSE, COSTS OFF) SELECT * FROM ft1 t1 WHERE c3 IS NOT NULL; -- NullTest
EXPLAIN (VERBOSE, COSTS OFF) SELECT * FROM ft1 t1 WHERE round(abs(c1), 0) = 1; -- FuncExpr
EXPLAIN (VERBOSE, COSTS OFF) SELECT * FROM ft1 t1 WHERE c1 = -c1; -- OpExpr(l)
EXPLAIN (VERBOSE, COSTS OFF) SELECT * FROM ft1 t1 WHERE (c1 IS NOT NULL) IS DISTINCT FROM (c1 IS NOT NULL); -- DistinctExpr
EXPLAIN (VERBOSE, COSTS OFF) SELECT * FROM ft1 t1 WHERE (c3 IS NOT NULL) IS DISTINCT FROM (c3 IS NOT NULL); -- DistinctExpr
EXPLAIN (VERBOSE, COSTS OFF) SELECT * FROM ft1 t1 WHERE c1 = ANY(ARRAY[c2, 1, c1 + 0]); -- ScalarArrayOpExpr
EXPLAIN (VERBOSE, COSTS OFF) SELECT * FROM ft1 t1 WHERE c1 = (ARRAY[c1,c2,3])[1]; -- SubscriptingRef
EXPLAIN (VERBOSE, COSTS OFF) SELECT * FROM ft1 t1 WHERE c6 = E'foo''s\\bar'; -- check special chars