mssql function sample

CREATE FUNCTION [dbo].[----]
               (@p_user_id VARCHAR(20),
                   @p_type VARCHAR(10))
RETURNS VARCHAR(100)
AS
  BEGIN
    DECLARE  @res VARCHAR(100)
    IF @p_type = 'USER_NAME'
      BEGIN
        SELECT @res = user_name
          FROM employee
         WHERE user_id = @p_user_id
      END
    ELSE
      IF @p_type = 'DEPT_ID'
        BEGIN
          SELECT @res = dept_id
            FROM employee
           WHERE user_id = @p_user_id
        END
      ELSE
        IF @p_type = 'DEPT_NAME'
          BEGIN
            SELECT @res = t2.dept_name
              FROM employee t1,
                   department t2
             WHERE t1.dept_id = t2.dept_id
               AND t1.user_id = @p_user_id
          END
    RETURN @res
  END