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copied!<p>Mysql definitely considers a full table scan cheaper than using the index; you can however force to use your primary key as preferred index with:</p> <pre> mysql> EXPLAIN SELECT * FROM userapplication FORCE INDEX (PRIMARY) WHERE application_id > 10; +----+-------------+-----------------+-------+---------------+---------+---------+------+------+-------------+ | id | select_type | table | type | possible_keys | key | key_len | ref | rows | Extra | +----+-------------+-----------------+-------+---------------+---------+---------+------+------+-------------+ | 1 | SIMPLE | userapplication | range | PRIMARY | PRIMARY | 4 | NULL | 24 | Using where | +----+-------------+-----------------+-------+---------------+---------+---------+------+------+-------------+ </pre> <p>Note that using "USE INDEX" instead of "FORCE INDEX" to only hint mysql on the index to use, mysql still prefers a full table scan:</p> <pre> mysql> EXPLAIN SELECT * FROM userapplication USE INDEX (PRIMARY) WHERE application_id > 10; +----+-------------+-----------------+------+---------------+------+---------+------+------+-------------+ | id | select_type | table | type | possible_keys | key | key_len | ref | rows | Extra | +----+-------------+-----------------+------+---------------+------+---------+------+------+-------------+ | 1 | SIMPLE | userapplication | ALL | PRIMARY | NULL | NULL | NULL | 34 | Using where | +----+-------------+-----------------+------+---------------+------+---------+------+------+-------------+ </pre>

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