I made some quick test to show what I mean by "performance problem". Note that I'm not saying the the first and the second test cases should perform equally. But there is too much difference - see the conclusion. 1) MariaDB [test]> SELECT BENCHMARK(50000000, (SELECT 1)); +---------------------------------+ | BENCHMARK(50000000, (SELECT 1)) | +---------------------------------+ | 0 | +---------------------------------+ 1 row in set (0.42 sec) 2) DELIMITER || CREATE FUNCTION f() RETURNS TINYINT BEGIN RETURN 1; END || DELIMITER ; MariaDB [test]> SELECT BENCHMARK(50000000, (SELECT f())); +-----------------------------------+ | BENCHMARK(50000000, (SELECT f())) | +-----------------------------------+ | 0 | +-----------------------------------+ 1 row in set (2 min 5.70 sec) 3) DELIMITER || CREATE FUNCTION f(x TINYINT) RETURNS TINYINT BEGIN RETURN x; END || DELIMITER ; MariaDB [test]> SELECT BENCHMARK(50000000, (SELECT f(1))); +------------------------------------+ | BENCHMARK(50000000, (SELECT f(1))) | +------------------------------------+ | 0 | +------------------------------------+ 1 row in set (3 min 35.20 sec) -- Conclusions: Times in seconds: 0.42 125.70 215.20 I don't know which ratio would be acceptable, but the difference betweem a trivial query and a trivial function is too high. Also, the difference between 2) and 3) is that the function in 3) accepts and returns a parameter. Again, the performance difference seems to me too high. Regards Federico