Alter a SQL server function to accept new optional parameter

sql

default-values

function-logic

sql-server-functions

byAlex Kataev·Oct 4, 2024

You can alter your SQL Server function by initializing an optional parameter with a default value, in this case NULL.

ALTER FUNCTION dbo.FuncName (@Param1 INT, @NewOptionalParam INT = NULL) RETURNS INT
AS
BEGIN
  -- Time to play hide and seek! The optional parameter will only come out if it's called.
  IF @NewOptionalParam IS NOT NULL
    -- Here we go! Include new behavior with @NewOptionalParam
  -- Rest of your function:
  RETURN @Result 
END

The syntax =@DefaultValue makes a parameter optional.

Making sense of optional parameters

When you alter a function to accept a new optional parameter, you are changing the behavior of that function. The function now needs to be prepared to work with or without an additional input. This can be a jigsaw puzzle at times, fitting the new piece without disrupting what's already there.

Setting default values

By specifying a default value for your new parameter, you allow for calls to this function without the need to pass this new argument. Default values should make sense in the context of your function's purpose:

@NewOptionalParam INT = 0   -- The new parameter's an integer? Zero could be a logical default.
@NewOptionalParam DATE = '19000101'   -- Date type? Let's start from the beginning of time!

Adapting function logic

Once you've introduced an optional parameter, you'd need to adjust your function logic to accommodate it. Here's a cheat sheet:

Use IF @NewOptionalParam IS NOT NULL to check before you start using it. No one likes null surprises!
Use COALESCE(@NewOptionalParam, 0) or ISNULL(@NewOptionalParam, 0) when the parameter could potentially participate in expressions.
When your optional parameter has the power to alter the functionality, be sure to update your stored queries or data retrieval steps.

Avoiding common missteps

Adjusting a function with optional parameters can be like walking a tightrope. Here are some safety nets:

Maintain backward compatibility. Old code likes to live undisturbed!
Double-check for null inputs. Nulls are like ninjas, they can sneak in when least expected!
Choose default values wisely. A random default value can lead to logic loopholes!

Difference between functions and stored procedures

Unlike a buffet in stored procedures, optional parameters in functions in SQL Server do not have the luxury of variety in behaviour. The DEFAULT keyword comes to our rescue:

SELECT dbo.YourFunction(@ExistingParam, DEFAULT);

Utilizing the DEFAULT keyword

When calling the function with the DEFAULT keyword, it's like telling SQL Server, "Fret not, use the default value I've provided!" This comes in handy when you want to skip optional parameters.

Tackling nullability

A good chef is always prepared! Your function needs to behave appropriately when the optional parameter is NULL, just like you'd have a Plan B if an ingredient is missing.

explain-codes / Sql / Alter a SQL server function to accept new optional parameter

Linked

Is it possible to have a default parameter for a mysql stored procedure?



Use current date as default value for a column



Modify Default value in SQL Server



Can parameterized statement stop all SQL injection?



Add a column with a default value to an existing table in SQL Server

