How Can I Pass a Table as a Parameter to a SQL Server UDF?

Passing Tables as Parameters to SQL Server UDFs

It is possible to pass a table as a parameter into a SQL Server scalar UDF. However, certain restrictions apply, as noted in the documentation: all data types are permitted except timestamp. To overcome this limitation, you can create user-defined table types (UDTTs).

Here's an example of a UDTT named TableType:

CREATE TYPE TableType
AS TABLE (
  LocationName VARCHAR(50)
);

With a UDTT defined, you can create a function that accepts a parameter of that type:

CREATE FUNCTION Example(@TableName TableType READONLY)
RETURNS VARCHAR(50)
AS
BEGIN
  DECLARE @name VARCHAR(50);

  SELECT TOP 1 @name = LocationName FROM @TableName;
  RETURN @name;
END;

Note that the parameter is defined as READONLY. To use this function, you can create a variable of the UDTT and insert data into it:

DECLARE @myTable TableType;
INSERT INTO @myTable(LocationName) VALUES('aaa');
SELECT * FROM @myTable;

Now you can call the Example function and pass the variable as a parameter:

SELECT dbo.Example(@myTable);

For your specific requirement of returning a CSV list of values from a table, you can modify the function accordingly. Additionally, you can perform filtering within the function, such as checking for nulls and duplicates.

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