When should I use a composite index in MySQL?

The composite index can be used when we are using sub queries. The advantages of using composite index are in case of.

• Joining
• Filtering
• Selecting

The following is the syntax of index.

 index(column_name1,column_name2,column_name3,column_name4,............................N) 

Let us create a table first and within that we have set index.

 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) 

To check if the indexes are created successfully.

 mysql> show index from MultipleIndexDemo; 

The following is the output.

 +-------------------+------------+----------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+---------------+---------+ | 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)