How to use user defined table type in function for return?

To use a user-defined table type in a function for return in SQL Server, you need to follow these steps:

1. Create the User-Defined Table Type: First, create the user-defined table type by defining the table structure. This can be done using a CREATE TYPE statement.

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CREATE TYPE dbo.EmployeeTableType AS TABLE (
    EmployeeId INT,
    FirstName NVARCHAR(50),
    LastName NVARCHAR(50),
    Department NVARCHAR(50)
);

2. Create the Function: Next, create the function that will use the user-defined table type as a return type. In the function definition, you can use the user-defined table type to return a table-like result.

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CREATE FUNCTION dbo.GetEmployees()
RETURNS dbo.EmployeeTableType -- Use the user-defined table type as return type
AS
BEGIN
    DECLARE @Result dbo.EmployeeTableType; -- Declare a variable of the user-defined table type

    INSERT INTO @Result (EmployeeId, FirstName, LastName, Department)
    SELECT EmployeeId, FirstName, LastName, Department
    FROM Employees; -- Replace with your actual table name

    RETURN @Result; -- Return the table variable
END;

3. Use the Function in Queries: Once the function is created, you can use it in queries as if it were a regular table. For example:

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SELECT * FROM dbo.GetEmployees();

The function will return a result set with the columns defined in the user-defined table type.

It's important to note that user-defined table types are only available in SQL Server, and this approach won't work with other database systems. Also, make sure to grant the necessary permissions to the function and the user-defined table type as per your security requirements.

Keep in mind that using user-defined table types can be beneficial in scenarios where you need to pass table-like data between stored procedures, functions, or other SQL components. However, using them in a function may not always be the best approach, especially if you want to return a result set from a complex query with joins or aggregations. In such cases, consider using views or stored procedures instead.