diff options
| author | Tomas Vondra <tomas.vondra@postgresql.org> | 2020-03-14 14:55:59 +0100 |
|---|---|---|
| committer | Tomas Vondra <tomas.vondra@postgresql.org> | 2020-03-14 16:12:41 +0100 |
| commit | 8f321bd16cdb11307f17007eb3c55b65d7d323ef (patch) | |
| tree | 0e344405ec07595d72156a2b7eff0e7d8255efa1 /doc/src | |
| parent | dbf95c843a3d66cf9a692f5937a1bec4f2261035 (diff) | |
| download | postgresql-8f321bd16cdb11307f17007eb3c55b65d7d323ef.tar.gz postgresql-8f321bd16cdb11307f17007eb3c55b65d7d323ef.zip | |
Use functional dependencies to estimate ScalarArrayOpExpr
Until now functional dependencies supported only simple equality clauses
and clauses that can be trivially translated to equalities. This commit
allows estimation of some ScalarArrayOpExpr (IN/ANY) clauses.
For IN clauses we can do this thanks to using operator with equality
semantics, which means an IN clause
WHERE c IN (1, 2, ..., N)
can be translated to
WHERE (c = 1 OR c = 2 OR ... OR c = N)
IN clauses are now considered compatible with functional dependencies,
and rely on the same assumption of consistency of queries with data
(which is an assumption we already used for simple equality clauses).
This applies also to ALL clauses with an equality operator, which can be
considered equivalent to IN clause.
ALL clauses are still considered incompatible, although there's some
discussion about maybe relaxing this in the future.
Author: Pierre Ducroquet
Reviewed-by: Tomas Vondra, Dean Rasheed
Discussion: https://www.postgresql.org/message-id/flat/13902317.Eha0YfKkKy%40pierred-pdoc
Diffstat (limited to 'doc/src')
| -rw-r--r-- | doc/src/sgml/perform.sgml | 3 |
1 files changed, 2 insertions, 1 deletions
diff --git a/doc/src/sgml/perform.sgml b/doc/src/sgml/perform.sgml index 0f61b0995d3..ab090441cfe 100644 --- a/doc/src/sgml/perform.sgml +++ b/doc/src/sgml/perform.sgml @@ -1203,7 +1203,8 @@ SELECT stxname, stxkeys, stxddependencies <para> Functional dependencies are currently only applied when considering - simple equality conditions that compare columns to constant values. + simple equality conditions that compare columns to constant values, + and <literal>IN</literal> clauses with constant values. They are not used to improve estimates for equality conditions comparing two columns or comparing a column to an expression, nor for range clauses, <literal>LIKE</literal> or any other type of condition. |