Sql – Optional parameters in SQL UDF without DEFAULT keyword

functionsqlsql-server

I am looking for a solution, how to create SQL UDF with optional params.

Pseudocode for function where Param1 is necessary and Param2 may be filled (but not needed):

dbo.myFnc(Param1 int [, Param2 int])

Is there a way to create thislike function? For existing built-in sample watch the STR function

STR ( float_expression [ , length [ , decimal ] ] )

Best Solution

You need to pass all arguments to functions, unlike stored procedures. You can use the default keyword to indicate that default value is to be used for the parameter, rather than a user-specified value.

So you can create your function like this:

CREATE FUNCTION dbo.myFnc
(
 @param1 int,
 @param2 int)

...

and then call the function like this:

dbo.myFnc(Param1, default)

Syntax:

ALTER TABLE {TABLENAME} 
ADD {COLUMNNAME} {TYPE} {NULL|NOT NULL} 
CONSTRAINT {CONSTRAINT_NAME} DEFAULT {DEFAULT_VALUE}
WITH VALUES

Example:

ALTER TABLE SomeTable
        ADD SomeCol Bit NULL --Or NOT NULL.
 CONSTRAINT D_SomeTable_SomeCol --When Omitted a Default-Constraint Name is autogenerated.
    DEFAULT (0)--Optional Default-Constraint.
WITH VALUES --Add if Column is Nullable and you want the Default Value for Existing Records.

Notes:

Optional Constraint Name:
If you leave out CONSTRAINT D_SomeTable_SomeCol then SQL Server will autogenerate
a Default-Contraint with a funny Name like: DF__SomeTa__SomeC__4FB7FEF6

Optional With-Values Statement:
The WITH VALUES is only needed when your Column is Nullable
and you want the Default Value used for Existing Records.
If your Column is NOT NULL, then it will automatically use the Default Value
for all Existing Records, whether you specify WITH VALUES or not.

How Inserts work with a Default-Constraint:
If you insert a Record into SomeTable and do not Specify SomeCol's value, then it will Default to 0.
If you insert a Record and Specify SomeCol's value as NULL (and your column allows nulls),
then the Default-Constraint will not be used and NULL will be inserted as the Value.

Notes were based on everyone's great feedback below.
Special Thanks to:
@Yatrix, @WalterStabosz, @YahooSerious, and @StackMan for their Comments.

Python – Passing a dictionary to a function as keyword parameters

Figured it out for myself in the end. It is simple, I was just missing the ** operator to unpack the dictionary

So my example becomes:

d = dict(p1=1, p2=2)
def f2(p1,p2):
    print p1, p2
f2(**d)

Best Solution

Related Solutions

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

Syntax:

Example:

Notes:

Python – Passing a dictionary to a function as keyword parameters

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