请问“decode(dl_qual_2,0,0,dl_qual_1/dl_qual_2)”这一句总报错:not a group by expre

SELECT  a.sdate
        ,a.stime
        ,a.bsc_name
        ,a.cell_id
        ,decode(dl_qual_2,0,0,dl_qual_1/dl_qual_2)        yao                yao
FROM    z_coding  a
GROUP BY a.sdate
        ,a.stime
        ,a.bsc_name
        ,a.cell_id;