Add new MySQL table columns and create indexes?

To add a new MySQL table column and index, you can use ALTER TABLE command.

The syntax is as follows

ALTER TABLE yourTableName ADD COLUMN yourColumnName dataType,
ADD INDEX(yourColumnName );

To understand the above syntax, let us create a table. The query to create a table is as follows

mysql> create table AddColumnAndIndexDemo
   -> (
   -> Id int NOT NULL AUTO_INCREMENT PRIMARY KEY,
   -> Name varchar(100),
   -> Address varchar(200)
   -> );
Query OK, 0 rows affected (0.81 sec)

Now you can check the description of table. The query is as follows −

mysql> desc AddColumnAndIndexDemo;

The following is the output

+---------+--------------+------+-----+---------+----------------+
| Field   | Type         | Null | Key | Default | Extra          |
+---------+--------------+------+-----+---------+----------------+
| Id      | int(11)      | NO   | PRI | NULL    | auto_increment |
| Name    | varchar(100) | YES  |     | NULL    |                |
| Address | varchar(200) | YES  |     | NULL    |                |
+---------+--------------+------+-----+---------+----------------+
3 rows in set (0.03 sec)

The following is the query to add a new MySQL table column and index

mysql> alter table AddColumnAndIndexDemo add column Age int, add index(Age);
Query OK, 0 rows affected (1.81 sec)
Records: 0 Duplicates: 0 Warnings: 0

Check the table description once again. The query is as follows −

mysql> desc AddColumnAndIndexDemo;

The following is the output

+---------+--------------+------+-----+---------+----------------+
| Field   | Type         | Null | Key | Default | Extra          |
+---------+--------------+------+-----+---------+----------------+
| Id      | int(11)      | NO   | PRI | NULL    | auto_increment |
| Name    | varchar(100) | YES  |     | NULL    |                |
| Address | varchar(200) | YES  |     | NULL    |                |
| Age     | int(11)      | YES  | MUL | NULL    |                |
+---------+--------------+------+-----+---------+----------------+
4 rows in set (0.00 sec)

Check the index from table using SHOW command. The query is as follows −

mysql> show index from AddColumnAndIndexDemo;

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 |
+-----------------------+------------+----------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+---------------+---------+
| addcolumnandindexdemo | 0          | PRIMARY  | 1            | Id          | A         | 0           | NULL     | NULL   |      | BTREE      |         |               | YES     |
| addcolumnandindexdemo | 1          | Age      | 1            | Age         | A         | 0           | NULL     | NULL   | YES  | BTREE      |         |               | YES     |
+-----------------------+------------+----------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+---------------+---------+
2 rows in set (0.16 sec)