SQL Keyword - ALTER

ALTER Keyword

The Alter keyword is used when we want to modify something.

If we want to add a new column or delete any column, or if we want to change any procedure, or change any function, The alter command is used in all of the preceding scenarios.

The Alter command is used with another command like 'Alter Table', 'Alter Procedure', 'Alter Column', 'Alter Trigger', etc.

1) Alter Table

The ALTER TABLE command is used to add, delete, or modify columns in a table. It is also used to add, delete or modify the constraints.

Syntax

ALTER TABLE <TABLE_NAME> ADD <COLUMN_NAME> <DATATYPE>;

Example

ALTER TABLE Employee ADD Dept_Id Integer;

2) Alter Column

The ALTER Column command is used to change the data type of a column in a table.

Syntax

ALTER TABLE <TABLE_NAME> ALTER COLUMN <COLUMN_NAME> <DATATYPE>;

Example

ALTER TABLE Employee ALTER COLUMN Emp_DOB Date;

3) Alter Procedure

The ALTER Procedure command is used to modify a procedure.

Syntax

ALTER PROCEDURE <PROCEDURE_NAME>
AS
BEGIN
   <STATEMENTS>
END

Example

ALTER PROCEDURE Get_Employee
AS
BEGIN
   Select * From Employee;
END

4) Alter Trigger

The ALTER Trigger command is used to modify trigger.

Syntax

ALTER TRIGGER <TRIGGER_NAME>
ON <TABLE_NAME>
FOR <INSERT OR/AND UPDATE OR/AND DELETE>
AS 
BEGIN
  <STATEMENT>
END

Example

ALTER TRIGGER Track_Employee
ON Employee
FOR UPDATE 
AS 
BEGIN
  Select * from Employee;
END

Summary

The Alter keyword is used when we want to modify something like Table, Procedure, Column, Trigger, etc.

Next Recommended Reading Alter Table Statement in SQL Server