Fix ndistinct estimates with system attributes
When estimating the number of groups using extended statistics, the code
was discarding information about system attributes. This led to strange
situation that
SELECT 1 FROM t GROUP BY ctid;
could have produced higher estimate (equal to pg_class.reltuples) than
SELECT 1 FROM t GROUP BY a, b, ctid;
with extended statistics on (a,b). Fixed by retaining information about
the system attribute.
Backpatch all the way to 10, where extended statistics were introduced.
Author: Tomas Vondra
Backpatch-through: 10
Branch
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REL_13_STABLE
Details
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https://git.postgresql.org/pg/commitdiff/67251c82af87865989eb90c7e8f4546cc0d66e6d
Modified Files
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src/backend/utils/adt/selfuncs.c | 6 +++---
src/test/regress/expected/stats_ext.out | 2 +-
2 files changed, 4 insertions(+), 4 deletions(-)