何时应在 MySQL 中使用复合索引?
mysqlmysqli database
使用子查询时可以使用复合索引。使用复合索引的优点如下。
- 连接
- 过滤
- 选择
以下是索引的语法。
index(column_name1,column_name2,column_name3,column_name4,............................N)
让我们先创建一个表，然后在其中设置索引。
mysql> create table MultipleIndexDemo - > ( - > id int, - > FirstName varchar(100), - > LastName varchar(100), - > Address varchar(200), - > index(id,LastName,Address) - > ); Query OK, 0 rows affected (0.57 sec)
检查索引是否创建成功。
mysql> show index from MultipleIndexDemo;
以下是输出。
+-------------------+------------+----------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+---------------+---------+ | Table | Non_unique | Key_name | Seq_in_index | Column_name | Collation | Cardinality | Sub_part | Packed | Null | Index_type | Comment | Index_comment | Visible | +-------------------+------------+----------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+---------------+---------+ | multipleindexdemo | 1 | id | 1 | id | A | 0 | NULL | NULL | YES | BTREE | | | YES | | multipleindexdemo | 1 | id | 2 | LastName | A | 0 | NULL | NULL | YES | BTREE | | | YES | | multipleindexdemo | 1 | id | 3 | Address | A | 0 | NULL | NULL | YES | BTREE | | | YES | +-------------------+------------+----------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+---------------+---------+ 3 rows in set (0.18 sec)
