Optional vs Required parameters in Stored Procedures

7

July 29, 2019 by Kenneth Fisher

If you are executing a stored procedure with a bunch of parameters it can be a bit of a pain if you have to pass a value in for each of them. Fortunately, it’s pretty easy to make some parameters required and others optional. You simply give them a default value.

CREATE PROCEDURE LotsOfParams (@Param1 INT, @Param2 INT, @Param3 INT, 
			@Param4 INT=NULL, @Param5 INT=0, @Param6 INT=5)
AS
PRINT 1;
GO

The first three parameters are required and the next three aren’t. You’ll notice that any valid value is fine even NULL.

These work:

EXEC LotsOfParams 1, 2, 3;
EXEC LotsOfParams 1, 2, 3, 4;
EXEC LotsOfParams @Param1 = 1, @Param3 = 2, @Param2 = 3;

These don’t:

EXEC LotsOfParams 1, 2;
EXEC LotsOfParams @Param4 = 1, @Param5 = 2;
EXEC LotsOfParams 1, @Param4 = 1, @Param5 = 2;

A couple of things of note here.

  • If you don’t specify the parameter names then they are strictly in the defined order. (@Param1, @Param2, etc)
  • If you do specify parameter names then it doesn’t matter what order you put them in.
  • Regardless of what order you put the parameters in, and if they are named or not, all of the required parameters must be there.
  • This doesn’t seem to be the case for function calls. As far as I can tell there is no way to make a function parameter optional.
  • What do I do if I want a default for the parameter but I still want it to be required? Go the old fasioned route.
    ALTER PROCEDURE LotsOfParams (@Param1 INT, @Param2 INT, @Param3 INT, 
    			@Param4 INT=0, @Param5 INT=0, @Param6 INT=0)
    AS
    IF @Param4 IS NULL
    	SET @Param4 = 5;
    IF @Param5 IS NULL
    	SET @Param5 = 12;
    PRINT 1;
    GO

7 thoughts on “Optional vs Required parameters in Stored Procedures

  1. Siggy says:

    Dumb question that I can’t be bothered to check for myself at the moment,,,

    Do either of these work ?

    EXEC LotsOfParams 1, @Param2 = 2, @Param3 = 3;

    EXEC LotsOfParams @Param1 = 1, @Param2 = 2, 3;

  2. […] Kenneth Fisher takes us through procedure parameters: […]

  3. If a default parameter value is defined in the stored procedure, then simply use the DEFAULT keyword for said parameter in the EXEC statement. It is a lot cleaner than a bunch of IF NULL statements and is better for documentation.

    CREATE PROCEDURE LotsOfParams (@p1 int = 0, @p2 int = 0, @p3 int = 0)
    AS
    SET NOCOUNT ON;
    SELECT @p1 as [p1], @p2 as [p2], @p3 as [p3];
    GO

    If defaults are assigned to all parameters then you can run the proc by itself:

    EXEC LotsOfParams

    And if you need to modify just one parameter, you can supply just the one:

    EXEC LotsOfParams @p2 = 99

    But it is best to always supply all the parameters IMO to make the code easier to read:

    EXEC LotsOfParams @p1 = default, @p2 = 99, @p3 = default

    • I disagree. Just as an example what if you have 20 parameters? That could get really ugly. Honestly even with 2 or 3 parameters it doesn’t look that clean. And when you are reading the code “default” doesn’t mean a whole lot to anyone. Most people realize if you haven’t passed in a parameter you’ve accepted the default.

      • Don’t recall I’ve ever created a proc with 20 parameters other than upserts which would have few if any default parameters, so I guess I wouldn’t want to pass DEFAULT that many times either. A function with that many parameters would require a value or the keyword DEFAULT for each position as you noted.

        For your last bullet point, parameter checking like in PowerShell to prevent NULL, restrict to a range of values, etc. would save a lot of IF statements. Even the same options for default value or binding on a column would be an improvement–and using a custom function would provide a lot of flexibility (but probably wreak havoc on plan reuse).

        • I was specifically thinking of things like sp_WhoIsActive (24), sp_DBPermissions (12), sp_BlitzIndex (9). Utility functions mostly.

          I have to admit it would be nice, although in the end I don’t mind putting in code to test each parameter if needed. I can put in custom error handling if I want, put in default values based on other values (if needed, etc).

          All of that said, I have objections to putting the DEFAULT keyword in when you call a SP, I just find it kind of cumbersome.

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