insert into #tmp
    select t1.[item], t2.[item], t3.[item]
        from (select * from [dbo].[fn_SplitString]('3,4', ',')) t1
            join (select * from [dbo].[fn_SplitString]('1,2', ',')) t2 on t1.[idx] = t2.[idx]
            join (select * from [dbo].[fn_SplitString]('5,6', ',')) t3 on t1.[idx] = t3.[idx]