T-SQL User defined function overloading? - sql

Question

I understand that T-SQL is not object oriented. I need to write a set of functions that mimics method overloading in C#.
Is function overloading supported in T-SQL in any way? If there is a hack to do this, is it recommended?

Answer 1

No, there is no way to do this.
I recommend you revisit the requirement, as "make apples look like oranges" is often difficult to do, and of questionable value.

Answer 2

One thing I have done successfully is to write the function in such a way as to allow it to handle null values, and then call it with nulls in place of the parameters you would like to omit.
Example:
create function ActiveUsers
(
#departmentId int,
#programId int
)
returns int
as
begin
declare #count int
select #count = count(*)
from users
where
departmentId = isnull(#departmentId, departmentId)
and programId = isnull(#programId, programId)
return #count
end
go
Uses:
select ActiveUsers(1,3) -- users in department 1 and program 3
select ActiveUsers(null,3) -- all users in program 3, regardless of department
select ActiveUsers(null,null) -- all users

Answer 3

You could pass in a sql_variant, but it comes with all sorts of hazards around it; you can't really use strong typing like you can with OO languages and overloading.
If you need to find the base type within your function, you can use the SQL_VARIANT_PROPERTY function.

Answer 4

You can pass in an array of values within a single string and parse them out using this techique by Erland Sommarskog.
Create a function with a varchar(max) parameter or several if necessary, then have your parameter values in that string like:
param1;param2;parma3;param4
or
param1:type;param2:type;param3:type
or
calltype|param1;param2;param3
etc, you are only limited by your imagination...
Use the technique from the link to split apart this array and use program logic to use those values as you wish.

Answer 5

One solution would be to utilize the sql_variant data type. This example works as long as you use the same datatype for both values. Returns whatever datatype you send it.
create function dbo.Greater(
#val1 sql_variant
,#val2 sql_variant
) returns sql_variant
as
begin
declare #rV sql_variant
set #rV = case when #val1 >= #val2 then #val1
else #val2 end
return #rV
end
go

Answer 6

A solution I've had some luck with is either creating a number of functions that each takes a different data type - or casting all input to NVARCHAR(MAX).
1. creating a number of functions that each takes a different data type
CREATE FUNCTION [dbo].[FunctionNameDatetime2]
CREATE FUNCTION [dbo].[FunctionNameInt]
CREATE FUNCTION [dbo].[FunctionNameString] --(this is not a typo)
CREATE FUNCTION [dbo].[FunctionNameUniqueidentifier]
...
Problem: duplication of code, and a lot functions
2. Cast all input to NVARCHAR(MAX)
CREATE FUNCTION [dbo].[IntToNvarchar]
(
#Key INT
)
RETURNS NVARCHAR(MAX)
AS
BEGIN
RETURN ISNULL(CAST(#Key AS NVARCHAR), '');
END
CREATE FUNCTION [dbo].[FunctionName]
(
#Key NVARCHAR(MAX)
)
RETURNS CHAR(32)
AS
BEGIN
DECLARE #something CHAR(32)
do stuff ...
RETURN #something;
END
SELECT [dbo].[FunctionName]([dbo].[IntToNvarchar](25))
Problem: less elegant code than overloading

Answer 7

I overload Functions all the time, but I happen to know that these kind of issues are often highly dependent on platform.
On our DB2 system, I routinely overload like the following:
CREATE Function Schema1.F1 (parm date)
returns date
return date + 1month;
CREATE Function Schema1.F1 (parm timestamp)
returns date
return date(timestamp) + 1month;
This is actually quite useful when you have multiple queries which have similar formating requirements.
The only problem I have found about this so far, is you better be sure that you want the function because the standard drop function "schema"."name" fails because it cannot determine which function to drop. If anyone knows how to drop overloaded sql functions, let me know!