Robię prostego counta na tabelce A
select count(*) from tabelkA
+----------+ | count(*) | +----------+ | 4841445 | -------------- 1 row IN SET (1.46 sec) +----+-------------+------------+-------+---------------+-------------+---------+------+---------+-------------+ | id | select_type | TABLE | type | possible_keys | KEY | key_len | ref | rows | Extra | +----+-------------+------------+-------+---------------+-------------+---------+------+---------+-------------+ | 1 | SIMPLE | stats_cmts | INDEX | NULL | typ_odczytu | 1 | NULL | 4832416 | USING INDEX | +----+-------------+------------+-------+---------------+-------------+---------+------+---------+-------------+
SELECT count(*) FROM tabelkaB +----------+ | count(*) | +----------+ | 10510082 | +----------+ +----+-------------+-------+------+---------------+------+---------+------+------+------------------------------+ | id | select_type | TABLE | type | possible_keys | KEY | key_len | ref | rows | Extra | +----+-------------+-------+------+---------------+------+---------+------+------+------------------------------+ | 1 | SIMPLE | NULL | NULL | NULL | NULL | NULL | NULL | NULL | SELECT TABLES optimized away | +----+-------------+-------+------+---------------+------+---------+------+------+------------------------------+ 1 row IN SET (0.00 sec)
Jak widać drugie zapytanie mimi, że wykonane na x2 większej tabeli wykonuje się błyskawicznie..
Ktoś może powiedzieć czym to jest spowodowane ?
pzdr