Oracle基础知识：DECODE、NVL

select 1
from PMADW.GET_WX_DATAPUSH_NEW_CHECK A
INNER JOIN PMADW.V_EXCEPTION_QTY_MAIN B on DECODE( A.VALUE_NAME,B.V_QTY_CODE,1,B.PARENTID,1,0) = 1
    and A.DAY_ID = B.DAY_ID
    AND  B.N_GRANULARITY = 1
where A.DAY_ID = TO_DATE('{$yest}','yyyy-mm-dd')
    and A.IS_NEW = 0
    AND  EXISTS( SELECT value_name FROM PMADW.GET_WX_DATAPUSH_NEW_CHECK  t2
         WHERE  t2.DAY_ID = b.DAY_ID
         AND t2.value_name = nvl(b.parentid,b.V_QTY_CODE))
    AND  ROWNUM <=1

DECODE(a,b,1,c,2,0)
解释：
    switch(a){
        case b:
            return 1;
            break;
        case c:
            return 2;
            break;
        default:
            return 0;
    }

nvl(a,b)
解释：
    return (a != '') ? a : b;