sql server自定义函数

CREATE function [dbo].[f_testFunc](
     @v_id nvarchar(4000)
    ,@v_type nvarchar(4000)
 )
    returns NVARCHAR(4000) as
begin
    declare @str_res NVARCHAR(4000);
    declare @str_id NVARCHAR(4000);
    declare @str_code NVARCHAR(4000);
    declare @str_name NVARCHAR(4000);
    SELECT @str_id = a.id,@str_code = a.event_code,@str_name = a.event_name
    FROM app_event a 
    WHERE a.id = @v_id;
    IF(@v_type='id')
      RETURN @str_id
    IF(@v_type='code')
      RETURN @str_code
     IF(@v_type='name')
      RETURN @str_name
       
    return @str_name;
end

GO