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)