database/postgres
1
0
Fork 0
mirror of https://github.com/postgres/postgres.git synced 2025-09-03 15:22:11 +03:00
Code Activity

Identify simple column references in extended statistics

Browse Source 
Until now, when defining extended statistics, everything except a plain
column reference was treated as complex expression. So for example "a"
was a column reference, but "(a)" would be an expression. In most cases
this does not matter much, but there were a couple strange consequences.
For example

    CREATE STATISTICS s ON a FROM t;

would fail, because extended stats require at least two columns. But

    CREATE STATISTICS s ON (a) FROM t;

would succeed, because that requirement does not apply to expressions.
Moreover, that statistics object is useless - the optimizer will always
use the regular statistics collected for attribute "a".

So do a bit more work to identify those expressions referencing a single
column, and translate them to a simple column reference. Backpatch to
14, where support for extended statistics on expressions was introduced.

Reported-by: Justin Pryzby
Backpatch-through: 14
Discussion: https://postgr.es/m/20210816013255.GS10479%40telsasoft.com
This commit is contained in:
Tomas Vondra
2021-09-01 17:41:54 +02:00
parent d760d942c7
commit 50ba70a957
3 changed files with 34 additions and 6 deletions
Download Patch File Download Diff File Expand all files Collapse all files

2
src/test/regress/expected/stats_ext.out
View File

@@ -55,6 +55,8 @@ ERROR: duplicate expression in statistics definition
CREATE STATISTICS tst (unrecognized) ON x, y FROM ext_stats_test;
ERROR: unrecognized statistics kind "unrecognized"
-- incorrect expressions
CREATE STATISTICS tst ON (y) FROM ext_stats_test; -- single column reference
ERROR: extended statistics require at least 2 columns
CREATE STATISTICS tst ON y + z FROM ext_stats_test; -- missing parentheses
ERROR: syntax error at or near "+"
LINE 1: CREATE STATISTICS tst ON y + z FROM ext_stats_test;

1
src/test/regress/sql/stats_ext.sql
View File

@@ -41,6 +41,7 @@ CREATE STATISTICS tst ON (x || 'x'), (x || 'x'), (y + 1), (x || 'x'), (x || 'x')
CREATE STATISTICS tst ON (x || 'x'), (x || 'x'), y FROM ext_stats_test;
CREATE STATISTICS tst (unrecognized) ON x, y FROM ext_stats_test;
-- incorrect expressions
CREATE STATISTICS tst ON (y) FROM ext_stats_test; -- single column reference
CREATE STATISTICS tst ON y + z FROM ext_stats_test; -- missing parentheses
CREATE STATISTICS tst ON (x, y) FROM ext_stats_test; -- tuple expression
DROP TABLE ext_stats_test;