[MDEV-27762] last_query_cost is 0.00 for some queries Created: 2022-02-07  Updated: 2022-02-08

Status: Open
Project: MariaDB Server
Component/s: Optimizer
Affects Version/s: 10.4, 10.5
Fix Version/s: 10.5

Type: Bug Priority: Major
Reporter: Michael Widenius Assignee: Sergei Petrunia
Resolution: Unresolved Votes: 0
Labels: None


 Description   

CREATE TABLE t1 (a INT, b INT, KEY (a), KEY (a,b));
CREATE TABLE t2 (c INT, KEY (c));
 
SELECT * FROM t1 t1a JOIN t1 t1b;
 
INSERT INTO t2 VALUES (1),(2);
INSERT INTO t1 VALUES (1,2),(3,4),(5,6),(7,8),(9,10),(11,12);

SELECT *
FROM
  t1 JOIN
  (SELECT t1.a, t1.b FROM t1, t2 WHERE t1.b = t2.c GROUP BY t1.a, t1.b) as dt
WHERE
  t1.a = dt.a;

show status like "last_query_cost";
DROP TABLE t1, t2;

This will output:

Variable_name   Value
Last_query_cost 0.000000


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