Description:
A query involving a SOME quantified comparison may evaluate inconsistently between WHERE filtering and direct SELECT expression evaluation when the left-hand side is an ELT() expression returning NULL and the subquery reads from a PRIMARY KEY column.
In this case, ELT() returns NULL because its index argument is negative. Therefore, the quantified comparison should evaluate to UNKNOWN, and the outer IS NOT UNKNOWN test should evaluate to FALSE. However, the WHERE query and the direct SELECT expression evaluation produce inconsistent results.
Removing the PRIMARY KEY constraint makes the inconsistency disappear, suggesting that the issue is related to an index-based optimization path for SOME/ANY quantified comparisons combined with NULL semantics handling.
How to repeat:
CREATE TABLE t1135 (c1 DECIMAL(20,0) PRIMARY KEY);
INSERT IGNORE INTO t1135 (c1) VALUES (-64);
SELECT t1135.c1 FROM t1135 WHERE (ELT(-64, -64, 16, -64, t1135.c1) >= SOME (SELECT t1135.c1 FROM t1135) IS NOT UNKNOWN);
-- return 1 rows
SELECT SUM(count) FROM (SELECT ((ELT(-64, -64, 16, -64, t1135.c1) >= SOME (SELECT t1135.c1 FROM t1135)) IS NOT UNKNOWN) IS TRUE AS count FROM t1135) AS ta_norec;
-- return 0
