SQL ALTER TABLE Statement

The ALTER TABLE statement is used to add, delete, or modify columns in an existing table.

The ALTER TABLE statement is also used to add and drop various constraints on an existing table.

ALTER TABLE - ADD Column

To add a column in a table, use the following syntax:

ALTER TABLE table_name
ADD column_name datatype;

The following SQL adds an "Email" column to the "Customers" table:

ALTER TABLE Customers
ADD Email varchar(255);

To delete a column in a table, use the following syntax (notice that some database systems don't allow deleting a column):

ALTER TABLE table_name
DROP COLUMN column_name;

The following SQL deletes the "Email" column from the "Customers" table:

ALTER TABLE Customers
DROP COLUMN Email;

To change the data type of a column in a table, use the following syntax:

SQL Server / MS Access:

My SQL / Oracle (prior version 10G):

ALTER TABLE table_name
MODIFY COLUMN column_name datatype;