Mysql优化（3） 索引优化

下面我们为表t2创建一个索引：

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001 002 003 004 005 006 007 008 009 010 011

mysql> create index in_id on t2(id); Query OK, 0 rows affected (0.01 sec) Records: 0  Duplicates: 0  Warnings: 0   mysql> show index from t2; +-------+------------+----------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+ | Table | Non_unique | Key_name | Seq_in_index | Column_name | Collation | Cardinality | Sub_part | Packed | Null | Index_type | Comment | +-------+------------+----------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+ | t2    |          1 | in_id    |            1 | id          | A         |        NULL |     NULL | NULL   | YES  | BTREE      |         | +-------+------------+----------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+ 1 row in set (0.00 sec)

并插入1000万行的数据。

然后再用：

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001	explain select * from t2 where id=1;

或者

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001	desc select * from t2 where id=1;

查询其影响行数。决定其是否需要优化

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