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

Passing a Table as a Parameter to a SQL Server UDF

It is possible to pass a table as a parameter to a scalar UDF in SQL Server, utilizing user-defined table types.

Creating a User-Defined Table Type

Define a table type to represent the structure of your table parameter. For example:

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

Defining the UDF

Create a scalar UDF that takes a parameter of the user-defined table type. The parameter must be declared as READONLY. For instance:

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

Passing a Table Variable

In SQL Server, you can create a variable of the user-defined table type and populate it with data from a table. For example:

DECLARE @myTable TableType
INSERT INTO @myTable(LocationName) VALUES('aaa')

Usage

To use the UDF with a table variable, pass the variable as the parameter. For instance:

SELECT dbo.Example(@myTable)

Handling Duplicates and NULLs

To ensure there are no duplicates and NULLs in your table, you can include relevant checks within your UDF:

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

    SELECT TOP 1 @name = LocationName 
    FROM @TableName 
    WHERE LocationName IS NOT NULL AND LocationName NOT IN (SELECT LocationName FROM @TableName WHERE LocationName IS NULL OR LocationName = @name)
    RETURN @name
END

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