Changing Column in MySQL from int to double?

To change the column in MySQL from int to double you need to use ALTER TABLE command.

The syntax is as follows:

ALTER TABLE yourTableName modify column yourColumnName DOUBLE NOT NULL;

If you want NULL value then remove NOT NULL from the above syntax. The syntax is as follows:

ALTER TABLE yourTableName modify column yourColumnName DOUBLE;

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

mysql> create table IntToDoubleDemo
   -> (
   -> Id int NOT NULL AUTO_INCREMENT,
   -> Name varchar(10),
   -> CylinderVolume int,
   -> PRIMARY KEY(Id)
   -> );
Query OK, 0 rows affected (0.63 sec)

Check the description of the table using DESC command. The syntax is as follows:

DESC yourTableName;

Apply the above query for your table to get the description of the table:

mysql> desc IntToDoubleDemo;

The following is the output:

+----------------+-------------+------+-----+---------+----------------+
| Field          | Type        | Null | Key | Default | Extra          |
+----------------+-------------+------+-----+---------+----------------+
| Id             | int(11)     | NO   | PRI | NULL    | auto_increment |
| Name           | varchar(10) | YES  |     | NULL    |                |
| CylinderVolume | int(11)     | YES  |     | NULL    |                |
+----------------+-------------+------+-----+---------+----------------+
3 rows in set (0.18 sec)

Look at the above sample output, the field ‘CylinderVolume’ is a type of int. Now you can convert from int to double.

Change the column in MySQL from int to double. The query is as follows:

mysql> alter table IntToDoubleDemo MODIFY COLUMN CylinderVolume double NOT NULL;
Query OK, 0 rows affected (2.79 sec)
Records: 0 Duplicates: 0 Warnings: 0

Once again check the description of the table. The query is as follows:

mysql> desc IntToDoubleDemo\G

The following is the output:

*************************** 1. row ***************************
Field: Id
Type: int(11)
Null: NO
Key: PRI
Default: NULL
Extra: auto_increment
*************************** 2. row ***************************
Field: Name
Type: varchar(10)
Null: YES
Key:
Default: NULL
Extra:
*************************** 3. row ***************************
Field: CylinderVolume
Type: double
Null: NO
Key:
Default: NULL
Extra:
3 rows in set (0.00 sec)