MySQL EXPLAIN 关键字执行查询还是仅解释查询?
mysqlmysqli database
EXPLAIN 关键字说明 MySQL 如何执行查询。让我们首先创建一个表 −
mysql> create table DemoTable1375 -> ( -> Id int NOT NULL AUTO_INCREMENT PRIMARY KEY, -> FirstName varchar(20), -> INDEX FIRST_INDEX(FirstName) -> ); Query OK, 0 rows affected (0.73 sec)
使用 insert 命令在表中插入一些记录 −
mysql> insert into DemoTable1375(FirstName) values('Chris');
Query OK, 1 row affected (0.25 sec)
mysql> insert into DemoTable1375(FirstName) values('Bob');
Query OK, 1 row affected (0.09 sec)
mysql> insert into DemoTable1375(FirstName) values('Sam');
Query OK, 1 row affected (1.06 sec)
mysql> insert into DemoTable1375(FirstName) values('David');
Query OK, 1 row affected (0.09 sec)
使用 select 语句显示表中的所有记录 −
mysql> select * from DemoTable1375;
这将产生以下输出 −
+----+-----------+ | Id | FirstName | +----+-----------+ | 2 | Bob | | 1 | Chris | | 4 | David | | 3 | Sam | +----+-----------+ 4 rows in set (0.00 sec)
这是使用 MySQL EXPLAIN 的查询 −
mysql> explain select * from DemoTable1375;
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 | DemoTable1375 | NULL | index | NULL | FIRST_INDEX | 63 | NULL | 4 | 100.00 | Using index | +----+-------------+---------------+------------+-------+---------------+-------------+---------+------+------+----------+-------------+ 1 row in set, 1 warning (0.03 sec)
