optimizer_record_context=ON changes the query result: a virtual column read from a const table or by MIN/MAX has a wrong value

Likely cause: commit a873569a470e9372e64a8f5fd14c1d2efa4247fa (MDEV-40383), in widen_read_set_no_vcols(). CS 13.0.2, from before it, does not have the bug.

CREATE TABLE t1 (pk INT PRIMARY KEY, a INT, g INT AS (a * 10) VIRTUAL, KEY (g)) ENGINE=MyISAM;

INSERT INTO t1 (pk, a) VALUES (1, 1), (2, 2), (3, 3);

SET optimizer_record_context=ON;

SELECT g INTO @g FROM t1 WHERE pk = 2;

--let $g= query_get_value(SELECT @g AS g, g, 1)

if ($g != 20)

{

  --die With optimizer_record_context=ON, SELECT g FROM t1 WHERE pk = 2 gives $g, but g = a * 10 = 20

}

DROP TABLE t1;

Leads to:

mysqltest: At line 8: With optimizer_record_context=ON, SELECT g FROM t1 WHERE pk = 2 gives 0, but g = a * 10 = 20

Recording the optimizer context changes the query result. With optimizer_record_context=OFF, the query gives 20. With it on, SELECT * FROM t1 WHERE pk = 2 gives g 0, SELECT MAX(g) FROM t1 gives 0, and SELECT MAX(g) FROM t1 WHERE g < 25 gives 25. On an InnoDB table, SELECT g FROM t1 WHERE pk = 2 and SELECT MAX(g) FROM t1 give NULL. SELECT MAX(g) FROM t1 WHERE g > 22 AND g < 25 gives 25 on the optimized build, and on the debug build it hits an assertion:

mariadbd: /tmp/optimizer-scan/13.1_dbg/sql/field.cc:4659: virtual longlong Field_long::val_int(): Assertion `marked_for_read()' failed.

From the code it seems that widen_read_set_no_vcols() in sql/opt_context_store_replay.cc gives the table a read set with all stored columns and no virtual columns, also the virtual columns that the query reads. The const-table read and the MIN()/MAX() read then do not compute g, so the query uses the value that is in the record buffer.