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

 1 CREATE OR REPLACE VIEW V_RES_CBA AS
 2 SELECT /*+INDEX(SEG IDX_T_RES_ALLOSEG_ALLOID)*/
 3    ALLO.ALLOID AS RESID,
 4    NULL AS AWB, 
 5    ALLO.ALLOTMENT AS ALLO_ID, 
 6    DAYS.FDATE + NVL(SEG.DAYSDISP, 0) AS FDATE, 
 7    ALLO.SPECULD AS SPECULD 
 8     FROM T_RES_ALLO ALLO, T_RES_ALLOSEG SEG, V_FDATE DAYS
 9    WHERE ALLO.ALLOID = SEG.ALLOID
10      AND ((ALLO.ALLOIND = 'A' AND ALLO.ALLO_DATE = DAYS.FDATE) OR
11          (ALLO.ALLOIND = 'S' AND
12          NVL(ALLO.SDATE, ALLO.ALLO_DATE) = DAYS.FDATE)) 
13   UNION
14   SELECT /*+INDEX(SEG IDX_T_RES_ALLOSEG_ALLOID)*/
15    ALLO.ALLOID AS RESID,
16    NULL AS AWB, 
17    ALLO.ALLOTMENT AS ALLO_ID, 
18    DAYS.FDATE + NVL(SEG.DAYSDISP, 0) AS FDATE, 
19    ALLO.SPECULD AS SPECULD 
20     FROM T_RES_ALLO ALLO, T_RES_ALLOSEG SEG, V_FDATE DAYS
21    WHERE ALLO.ALLOID = SEG.ALLOID
22      AND ALLO.ALLO_DATE IS NULL
23      AND ALLO.ALLOIND = 'A'
24      AND (DAYS.FDATE >= ALLO.SDATE AND DAYS.FDATE <= ALLO.EDATE AND
25          INSTR(ALLO.WEEKDAY, DAYS.WEEKDAY) > 0) 
26      AND NOT EXISTS (SELECT subQuery.ALLOID
27             from T_RES_ALLO subQuery
28            where subQuery.ALLO_DATE = DAYS.FDATE
29              and subQuery.ALLOTMENT = ALLO.ALLOTMENT)
30 ;

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