使用 MySQL EXPLAIN KEYWORD 获取信息?
mysqlmysqli database
首先我们创建一个表 −
mysql> create table DemoTable1541 -> ( -> EmployeeId int, -> EmployeeFirstName varchar(20) NOT NULL -> ); Query OK, 0 rows affected (0.94 sec)
这是在列上创建索引的查询 −
mysql> create index emp_name_index on DemoTable1541(EmployeeFirstName); Query OK, 0 rows affected (0.75 sec) Records: 0 Duplicates: 0 Warnings: 0
使用 insert 命令在表中插入一些记录 −
mysql> insert into DemoTable1541 values(1,'Robert'); Query OK, 1 row affected (0.18 sec) mysql> insert into DemoTable1541 values(2,'Adam'); Query OK, 1 row affected (0.20 sec) mysql> insert into DemoTable1541 values(3,'Mike'); Query OK, 1 row affected (0.14 sec)
使用 select 语句显示表中的所有记录 −
mysql> select * from DemoTable1541;
这将产生以下输出 −
+------------+-------------------+ | EmployeeId | EmployeeFirstName | +------------+-------------------+ | 1 | Robert | | 2 | Adam | | 3 | Mike | +------------+-------------------+ 3 rows in set (0.00 sec)
以下是使用 EXPLAIN 的查询 −
mysql> explain select * from DemoTable1541 where EmployeeFirstName='Mike';
这将产生以下输出 −
+----+-------------+---------------+------------+------+----------------+----------------+---------+-------+------+----------+-------+ | id | select_type | table | partitions | type | possible_keys | key | key_len | ref | rows | filtered | Extra | +----+-------------+---------------+------------+------+----------------+----------------+---------+-------+------+----------+-------+ | 1 | SIMPLE | DemoTable1541 | NULL | ref | emp_name_index | emp_name_index | 62 | const | 1 | 100.00 | NULL | +----+-------------+---------------+------------+------+----------------+----------------+---------+-------+------+----------+-------+ 1 row in set, 1 warning (0.00 sec)
