Avoid mislabeling of lateral references when pulling up a subquery.
If we are pulling up a subquery that's under an outer join, and
the subquery's target list contains a strict expression that uses
both a subquery variable and a lateral-reference variable, it's okay
to pull up the expression without wrapping it in a PlaceHolderVar.
That's safe because if the subquery variable is forced to NULL
by the outer join, the expression result will come out as NULL too,
so we don't have to force that outcome by evaluating the expression
below the outer join. It'd be correct to wrap in a PHV, but that can
lead to very significantly worse plans, since we'd then have to use
a nestloop plan to pass down the lateral reference to where the
expression will be evaluated.
However, when we do that, we should not mark the lateral reference
variable as being nulled by the outer join, because it isn't after
we pull up the expression in this way. So the marking logic added
by cb8e50a4a was incorrect in this detail, leading to "wrong
varnullingrels" errors from the consistency-checking logic in
setrefs.c. It seems to be sufficient to just not mark lateral
references at all in this case. (I have a nagging feeling that more
complexity may be needed in cases where there are several levels of
outer join, but some attempts to break it with that didn't succeed.)
Per report from Bertrand Mamasam. Back-patch to v16, as the previous
patch was.
Discussion: https://postgr.es/m/CACZ67_UA_EVrqiFXJu9XK50baEpH=ofEPJswa2kFxg6xuSw-ww@mail.gmail.com
Branch
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REL_17_STABLE
Details
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https://git.postgresql.org/pg/commitdiff/72822a99d44f040e9776c892a8ab877a06c7b7ad
Modified Files
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src/backend/optimizer/prep/prepjointree.c | 19 +++++++++++--
src/test/regress/expected/subselect.out | 47 +++++++++++++++++++++++++++++++
src/test/regress/sql/subselect.sql | 16 +++++++++++
3 files changed, 80 insertions(+), 2 deletions(-)
