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The two statements have totally different performance: mysql> explain select * from jobs where createIndexed=false; +----+-------------+-------+------+----------------------+----------------------+---------+-------+------+-------+ | id | select_type | table | type | possible_keys | key | key_len | ref | rows | Extra | +----+-------------+-------+------+----------------------+----------------------+---------+-------+------+-------+ | 1 | SIMPLE | jobs | ref | i_jobs_createIndexed | i_jobs_createIndexed | 1 | const | 1 | | +----+-------------+-------+------+----------------------+----------------------+---------+-------+------+-------+ 1 row in set (0.01 sec) mysql> explain select * from jobs where !createIndexed; +----+-------------+-------+------+---------------+------+---------+------+-------+-------------+ | id | select_type | table | type | possible_keys | key | key_len | ref | rows | Extra | +----+-------------+-------+------+---------------+------+---------+------+-------+-------------+ | 1 | SIMPLE | jobs | ALL | NULL | NULL | NULL | NULL | 17996 | Using where | +----+-------------+-------+------+---------------+------+---------+------+-------+-------------+ Column definition and related index for aiding analysis: createIndexed tinyint(1) NOT NULL DEFAULT 0, create index i_jobs_createIndexed on jobs(createIndexed);

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