如何让oracle的select强制走索引


大多数情况下，oracle数据库内置的查询优化策略还是很成功的，但偶尔也有犯2的时候，即使有索引，也会做全表扫描，可以参考以下语句的写法，强制让select语句使用索引

CREATE OR REPLACE VIEW V_RES_CBA AS

SELECT /*+INDEX(SEG IDX_T_RES_ALLOSEG_ALLOID)*/

   ALLO.ALLOID AS RESID,

   NULL AS AWB,

   ALLO.ALLOTMENT AS ALLO_ID,

   DAYS.FDATE + NVL(SEG.DAYSDISP, 0) AS FDATE,

   ALLO.SPECULD AS SPECULD

    FROM T_RES_ALLO ALLO, T_RES_ALLOSEG SEG, V_FDATE DAYS

   WHERE ALLO.ALLOID = SEG.ALLOID

     AND ((ALLO.ALLOIND = 'A' AND ALLO.ALLO_DATE = DAYS.FDATE) OR

         (ALLO.ALLOIND = 'S' AND

         NVL(ALLO.SDATE, ALLO.ALLO_DATE) = DAYS.FDATE))

  UNION

  SELECT /*+INDEX(SEG IDX_T_RES_ALLOSEG_ALLOID)*/

   ALLO.ALLOID AS RESID,

   NULL AS AWB,

   ALLO.ALLOTMENT AS ALLO_ID,

   DAYS.FDATE + NVL(SEG.DAYSDISP, 0) AS FDATE,

   ALLO.SPECULD AS SPECULD

    FROM T_RES_ALLO ALLO, T_RES_ALLOSEG SEG, V_FDATE DAYS

   WHERE ALLO.ALLOID = SEG.ALLOID

     AND ALLO.ALLO_DATE IS NULL

     AND ALLO.ALLOIND = 'A'

     AND (DAYS.FDATE >= ALLO.SDATE AND DAYS.FDATE <= ALLO.EDATE AND

         INSTR(ALLO.WEEKDAY, DAYS.WEEKDAY) > 0)

     AND NOT EXISTS (SELECT subQuery.ALLOID

            from T_RES_ALLO subQuery

           where subQuery.ALLO_DATE = DAYS.FDATE

             and subQuery.ALLOTMENT = ALLO.ALLOTMENT)

;

要点：

1、/*+INDEX(SEG IDX_T_RES_ALLOSEG_ALLOID)*/
这里的/*...*/中间不要有空格

2、表名要用别名，即：以上面的sql语句为例，要使用SEG，而不是T_RES_ALLOSEG