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.ALLOID10      AND ((ALLO.ALLOIND = 'A' AND ALLO.ALLO_DATE = DAYS.FDATE) OR11          (ALLO.ALLOIND = 'S' AND12          NVL(ALLO.SDATE, ALLO.ALLO_DATE) = DAYS.FDATE)) 13   UNION14   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 DAYS21    WHERE ALLO.ALLOID = SEG.ALLOID22      AND ALLO.ALLO_DATE IS NULL23      AND ALLO.ALLOIND = 'A'24      AND (DAYS.FDATE >= ALLO.SDATE AND DAYS.FDATE <= ALLO.EDATE AND25          INSTR(ALLO.WEEKDAY, DAYS.WEEKDAY) > 0) 26      AND NOT EXISTS (SELECT subQuery.ALLOID27             from T_RES_ALLO subQuery28            where subQuery.ALLO_DATE = DAYS.FDATE29              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