Fix constant-folding of ROW(...) IS [NOT] NULL with composite fields.
The SQL standard appears to specify that IS [NOT] NULL's tests of field
nullness are non-recursive, ie, we shouldn't consider that a composite
field with value ROW(NULL,NULL) is null for this purpose.
ExecEvalNullTest got this right, but eval_const_expressions did not,
leading to weird inconsistencies depending on whether the expression
was such that the planner could apply constant folding.
Also, adjust the docs to mention that IS [NOT] DISTINCT FROM NULL can be
used as a substitute test if a simple null check is wanted for a rowtype
argument. That motivated reordering things so that IS [NOT] DISTINCT FROM
is described before IS [NOT] NULL. In HEAD, I went a bit further and added
a table showing all the comparison-related predicates.
Per bug #14235. Back-patch to all supported branches, since it's certainly
undesirable that constant-folding should change the semantics.
Report and patch by Andrew Gierth; assorted wordsmithing and revised
regression test cases by me.
Report: <20160708024746.1410.57282@wrigleys.postgresql.org>
Branch
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REL9_5_STABLE
Details
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http://git.postgresql.org/pg/commitdiff/d2ef7758d2d2175509b2f49f7049e06ccd81fd57
Modified Files
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doc/src/sgml/func.sgml | 70 +++++++++++++++++-----------------
src/backend/executor/execQual.c | 15 ++++++++
src/backend/optimizer/util/clauses.c | 13 +++++--
src/test/regress/expected/rowtypes.out | 54 ++++++++++++++++++++++++++
src/test/regress/sql/rowtypes.sql | 24 ++++++++++++
5 files changed, 136 insertions(+), 40 deletions(-)