SQL ALTER COLUMN Keyword

The SQL ALTER COLUMN keyword is used to change the data type of a column in an existing table.

Syntax

The syntax for using ALTER COLUMN statement to modify datatype of a column is given below:

/* SQL Server / MS Access */
ALTER TABLE table_name
ALTER COLUMN column_name datatype;

/* MySQL / Oracle (prior 10G version) */
ALTER TABLE table_name
MODIFY COLUMN column_name datatype;

/* Oracle 10G and later */
ALTER TABLE table_name
MODIFY column_name datatype;

Example:

Consider a database table called Employee with the following records:

In this table, the datatype of City column is VARCHAR(100). To change the datatype of the column to VARCHAR(255), the SQL code is given below:

/* SQL Server / MS Access */
ALTER TABLE Employee
ALTER COLUMN City VARCHAR(255);

/* MySQL / Oracle (prior 10G version) */
ALTER TABLE Employee
MODIFY COLUMN City VARCHAR(255);

/* Oracle 10G and later */
ALTER TABLE Employee
MODIFY City VARCHAR(255);

This will change the datatype of City column from VARCHAR(100) to VARCHAR(255). For a complete reference of all the data types available in SQL database, see Data Types reference.