MySQL Explain详解

核心提示： (6).SUBQUERY子查询中的第一个select.mysql>explainselect*fromt3whereid=(selectidfromt3whereid=3952602);++-+---+---+---+-+-+---+--+-+|id|select_type|tabl

(6).SUBQUERY

子查询中的第一个select.

mysql>explainselect*fromt3whereid=(selectidfromt3whereid=3952602);　
　　+----+-------------+-------+-------+-------------------+---------+---------+-------+------+-------------+　
　　|id|select_type|table|type|possible_keys|key|key_len|ref|rows|Extra|　
　　+----+-------------+-------+-------+-------------------+---------+---------+-------+------+-------------+　
　　|1|PRIMARY|t3|const|PRIMARY,idx_t3_id|PRIMARY|4|const|1||　
　　|2|SUBQUERY|t3|const|PRIMARY,idx_t3_id|PRIMARY|4||1|Usingindex|　
　　+----+-------------+-------+-------+-------------------+---------+---------+-------+------+-------------+

(7). DEPENDENT SUBQUERY

子查询中的第一个select，取决于外面的查询。

mysql>explainselectidfromt3whereidin(selectidfromt3whereid=3952602);　
　　+----+--------------------+-------+-------+-------------------+---------+---------+-------+------+--------------------------+　
　　|id|select_type|table|type|possible_keys|key|key_len|ref|rows|Extra|　
　　+----+--------------------+-------+-------+-------------------+---------+---------+-------+------+--------------------------+　
　　|1|PRIMARY|t3|index|NULL|PRIMARY|4|NULL|1000|Usingwhere;Usingindex|　
　　|2|DEPENDENTSUBQUERY|t3|const|PRIMARY,idx_t3_id|PRIMARY|4|const|1|Usingindex|　
　　+----+--------------------+-------+-------+-------------------+---------+---------+-------+------+--------------------------+

(8).DERIVED