RAISERROR in SQL SERVER

RAISERROR will use the built-in messages in sys.messages view or dynamically generated error message.

The Syntax is as follows
RAISERROR ( { msg_id | msg_str | @local_variable }    
{ ,severity ,state }     
[ ,argument [ ,...n ] ] )     [ WITH option [ ,...n ] ]

Severity 0 – 18 , Can be raised by any user

Severity 19 – 25, Can be raised by those who have sysadmin role.

State : This is a integer value between 0 to 255

The below shows an error message if the employee id does not exists

CREATE PROCEDURE GenerateError(@EmployeeID int)
AS
BEGIN
If exists(SELECT 1 FROM employee WHERE EmployeeID = @EmployeeID)
BEGIN
SELECT * FROM Employee WHERE EmployeeID = @EmployeeID
END
ELSE
BEGIN
RAISERROR ('Employee ID does not exists', 10, 2)
END
END