Creating a UDF(User Define Function) if is does not exist and skipping it if it exists

Hi and thanks for reading this.

I am trying to use the IF EXISTS/IF NOT EXISTS statement to check if an Object exist. Basically I want to skip it if it is there or create it if it is not there.

I have writing the code in two different ways but I get an error: Create function must be the only function in the batch. If I place GO between the statements as Illustrated below, I get another warning: Incorrect Syntax near GO.

Where am I going wrong here?

IF NOT EXISTS
(select * from Information_schema.Routines where SPECIFIC_SCHEMA='dbo' 
AND SPECIFIC_NAME = 'FMT_PHONE_NBR' AND Routine_Type='FUNCTION')

/*CREATE FUNCTION TO FORMAT PHONE NUMBERS*/
CREATE FUNCTION [dbo].[FMT_PHONE_NBR](@phoneNumber VARCHAR(12))
RETURNS VARCHAR(12)
AS
BEGIN
    RETURN SUBSTRING(@phoneNumber, 1, 3) + '-' + 
           SUBSTRING(@phoneNumber, 4, 3) + '-' + 
           SUBSTRING(@phoneNumber, 7, 4)
END

GO

Or this:

IF NOT EXISTS
(SELECT name FROM sys.objects WHERE name = 'dbo.FMT_PHONE_NBR')

GO

/*CREATE FUNCTION TO FORMAT PHONE NUMBERS*/
CREATE FUNCTION [dbo].[FMT_PHONE_NBR](@phoneNumber VARCHAR(12))
RETURNS VARCHAR(12)
AS
BEGIN
    RETURN SUBSTRING(@phoneNumber, 1, 3) + '-' + 
           SUBSTRING(@phoneNumber, 4, 3) + '-' + 
           SUBSTRING(@phoneNumber, 7, 4)
END

GO

Thanks for checking this out!

Answer

The easiest way to solve this is actually to delete the function if it already exists, and then re-create it:

/* If we already exist, get rid of us, and fix our spelling */
IF OBJECT_ID('dbo.FMT_PHONE_NBR') IS NOT NULL
  DROP FUNCTION FMT_PHONE_NBR
GO

/*CREATE FUNCTION TO FORMAT PHONE NUMBERS*/
CREATE FUNCTION [dbo].[FMT_PHONE_NBR](@phoneNumber VARCHAR(12))
RETURNS VARCHAR(12)
AS
BEGIN
    RETURN SUBSTRING(@phoneNumber, 1, 3) + '-' + 
           SUBSTRING(@phoneNumber, 4, 3) + '-' + 
           SUBSTRING(@phoneNumber, 7, 4)
END

GO

Note the usage of the ‘object_id’ function in the above. This is actually a pretty common way to check for the existence of an object, although it is subject to certain constraints.

You can read more about it here: OBJECT_ID