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Do not reduce subquery output row count estimates due to DISTINCT until

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after the decision of whether or not to use an index for ORDER BY has been
made.

FossilOrigin-Name: 27390051e86ad86fb35219329d359be9e83073f59782631af7fc519225e10565
This commit is contained in:
drh
2023-09-15 19:00:47 +00:00
parent 20220d4682
commit c09701db9b
4 changed files with 61 additions and 19 deletions
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43
test/subquery.test
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@ -11,8 +11,6 @@
# This file implements regression tests for SQLite library. The
# focus of this script is testing correlated subqueries
#
# $Id: subquery.test,v 1.17 2009/01/09 01:12:28 drh Exp $
#
set testdir [file dirname $argv0]
source $testdir/tester.tcl
@ -613,4 +611,45 @@ do_execsql_test subquery-9.4 {
SELECT (SELECT DISTINCT x FROM t1 ORDER BY +x LIMIT 1 OFFSET 2) FROM t1;
} {{} {} {} {}}
# 2023-09-15
# Query planner performance regression reported by private email
# on 2023-09-14, caused by VIEWSCAN optimization of check-in 609fbb94b8f01d67
# from 2022-09-01.
#
reset_db
do_execsql_test subquery-10.1 {
CREATE TABLE t1(aa TEXT, bb INT, cc TEXT);
CREATE INDEX x11 on t1(bb);
CREATE INDEX x12 on t1(aa);
CREATE TABLE t2(aa TEXT, xx INT);
ANALYZE sqlite_master;
INSERT INTO sqlite_stat1(tbl, idx, stat) VALUES('t1', 'x11', '156789 28');
INSERT INTO sqlite_stat1(tbl, idx, stat) VALUES('t1', 'x12', '156789 1');
ANALYZE sqlite_master;
}
do_eqp_test subquery-10.2 {
WITH v1(aa,cc,bb) AS (SELECT aa, cc, bb FROM t1 WHERE bb=12345),
v2(aa,mx) AS (SELECT aa, max(xx) FROM t2 GROUP BY aa)
SELECT * FROM v1 JOIN v2 ON v1.aa=v2.aa;
} {
QUERY PLAN
|--CO-ROUTINE v2
| |--SCAN t2
| `--USE TEMP B-TREE FOR GROUP BY
|--SEARCH t1 USING INDEX x11 (bb=?)
`--SEARCH v2 USING AUTOMATIC COVERING INDEX (aa=?)
}
# ^^^^^^^^^^^^^
# Prior to the fix the incorrect (slow) plan caused by the
# VIEWSCAN optimization was:
#
# QUERY PLAN
# |--CO-ROUTINE v2
# | |--SCAN t2
# | `--USE TEMP B-TREE FOR GROUP BY
# |--SCAN v2
# `--SEARCH t1 USING INDEX x12 (aa=?)
#
finish_test