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Improved estimate on the number of output rows in a recursive common table expression

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that uses the UNION operator.  Follow-up to [f911f1c4977fbcae] and it's output row
estimate changes associated with DISTINCT queries.

FossilOrigin-Name: 92513f6bce7ecc778e78af3a77bc66ff65585fffa2e3138f8acb9e617121eeb0
This commit is contained in:
drh
2025-04-14 19:43:30 +00:00
parent c801f8954e
commit 483e1181c5
5 changed files with 56 additions and 11 deletions
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38
test/subquery.test
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@ -650,6 +650,44 @@ do_eqp_test subquery-10.2 {
# |--SCAN v2
# `--SEARCH t1 USING INDEX x12 (aa=?)
#
#---------------------------------------------------------------------------
# Follow-up on 2025-04-14. Performance issue found while working
# on Fossil (Fossil check-in 2025-04-13T19:54).
#
do_execsql_test 10.3 {
CREATE TABLE blob(
rid INTEGER PRIMARY KEY,
size INT,
uuid TEXT
);
CREATE TABLE delta(
rid INTEGER PRIMARY KEY,
srcid INT
);
CREATE INDEX delta_i1 ON delta(srcid);
}
do_eqp_test subquery-10.4 {
WITH RECURSIVE deltasof(rid) AS (
SELECT rid FROM delta WHERE srcid=125020
UNION
SELECT delta.rid FROM deltasof, delta
WHERE delta.srcid=deltasof.rid)
SELECT deltasof.rid, blob.uuid FROM deltasof, blob
WHERE blob.rid=deltasof.rid;
} {
QUERY PLAN
|--CO-ROUTINE deltasof
| |--SETUP
| | `--SEARCH delta USING COVERING INDEX delta_i1 (srcid=?)
| `--RECURSIVE STEP
| |--SCAN deltasof
| `--SEARCH delta USING COVERING INDEX delta_i1 (srcid=?)
|--SCAN deltasof
`--SEARCH blob USING INTEGER PRIMARY KEY (rowid=?)
}
# ^^^^^^^^^^^^^^^^^^
# deltasof should be the outer loop and blob the inner loop
# Prior to the fix, SQLite was doing it the other way around.
#-----------------------------------------------------------------------------
# 2024-04-25 Column affinities for columns of compound subqueries