DEVELOPER SITE
HTMLCSSJAVASCRIPTSQLPHPBOOTSTRAPJQUERYANGULARXML
 
medianet_width = "728"; medianet_height = "90"; medianet_crid = "246671083"; medianet_versionId = "3111299";

SQL ALTER TABLE Statement


ALTER TABLE statement

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

SQL ALTER TABLE syntax

To add columns to the table, use the following syntax:

ALTER TABLE table_name
ADD column_name datatype

To delete columns from a table, use the following syntax (note that some database systems do not allow this method of deleting columns from a database table):

ALTER TABLE table_name
DROP COLUMN column_name

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

SQL Server /MS Access:

ALTER TABLE table_name
ALTER COLUMN column_name datatype

My SQL /Oracle:

ALTER TABLE table_name
MODIFY COLUMN column_name datatype

After Oracle 10G:

  ALTER TABLE table_name
MODIFY column_name datatype  ;  


SQL ALTER TABLE example

See the "Persons" table:

P_Id LastName FirstName Address City
1 Hansen Ola Timoteivn 10 Sandnes
2 Svendson Tove Borgvn 23 Sandnes
3 Pettersen Kari Storgt 20 Stavanger

Now we want to add a column named "DateOfBirth" to the "Persons" table.

We use the following SQL statement:

ALTER TABLE Persons
ADD DateOfBirth date

Please note that the new column "DateOfBirth" is of type date and can hold dates. The data type specifies the type of data that can be stored in a column. To learn about the data types available in MS Access, MySQL, and SQL Server, visit our complete Data Types Reference Manual .

The "Persons" table will now look like this:

P_Id LastName FirstName Address City DateOfBirth
1 Hansen Ola Timoteivn 10 Sandnes
2 Svendson Tove Borgvn 23 Sandnes
3 Pettersen Kari Storgt 20 Stavanger


Change data type instance

Now we want to change the data type of the "DateOfBirth" column in the "Persons" table.

We use the following SQL statement:

ALTER TABLE Persons
ALTER COLUMN DateOfBirth year

Please note that the "DateOfBirth" column is now of type year and can hold a 2- or 4-digit year.


DROP COLUMN example

Next, we want to delete the "DateOfBirth" column in the "Person" table.

We use the following SQL statement:

ALTER TABLE Persons
DROP COLUMN DateOfBirth

The "Persons" table will now look like this:

P_Id LastName FirstName Address City
1 Hansen Ola Timoteivn 10 Sandnes
2 Svendson Tove Borgvn 23 Sandnes
3 Pettersen Kari Storgt 20 Stavanger