下面是一张报表的SQL实现，不用深入业务，你可以看到上面的4条SQL和下面的4条SQL其实大致相同，只是部分条件不一样，想要优化的第一感觉是如何减少扫描的次数，这个时候case when就派上用场了。
SELECT DECODE(ALL_COUNT, 0, 0, ROUND(ARRIVED_COUNT / ALL_COUNT, 4) * 100) ARRIVED_RATE
FROM (SELECT E.COUNT_RESULT + F.COUNT_RESULT + G.COUNT_RESULT +
H.COUNT_RESULT ARRIVED_COUNT
FROM (SELECT COUNT(1) COUNT_RESULT
FROM GG_TASK_WORK_SHEET PTWS,
GG_TASK_PATROL_SHEET_DETAIL PSD,
GG_PATROL_WORK_POINT PPWP,
GG_PATROL_POINT PPP,
GG_PATROL_EQUIPMENT PPE
WHERE PTWS.WORK_SHEET_ID = PSD.WORK_SHEET_ID
AND TO_CHAR(PTWS.WORK_SHEET_ID) = PPWP.WORK_ID
AND PPWP.PATROL_POINT_ID = PPP.PATROL_POINT_ID
AND PPP.PATROL_POINT_ID = PPE.PATROL_POINT_ID
AND PTWS.TASK_TYPE = 4
AND PTWS.SHEET_TYPE = 2
AND PSD.PATROL_TYPE <> -1
AND PSD.IS_NEED_PDA = '1'
AND PPWP.PATROL_FLAG = 1
AND PTWS.IS_COMPLETE = '3'
AND TO_CHAR(PTWS.REAL_END_DATE, 'YYYY') = '2013'
AND PPE.DEVICE_ID = 1003551930) E,
(SELECT COUNT(1) COUNT_RESULT
FROM GG_TASK_WORK_SHEET PTWS,
GG_TASK_PATROL_SHEET_DETAIL PSD,
GG_PATROL_WORK_POINT PPWP,
GG_PATROL_POINT PPP,
GG_TASK_PATROL_OBJECT PTPO
WHERE PTWS.WORK_SHEET_ID = PSD.WORK_SHEET_ID
AND TO_CHAR(PTWS.WORK_SHEET_ID) = PPWP.WORK_ID
AND PPWP.PATROL_POINT_ID = PPP.PATROL_POINT_ID
AND PPP.PATROL_POINT_ID = PTPO.PATROL_POINT_ID
AND PTWS.TASK_TYPE = 4
AND PTWS.SHEET_TYPE = 2
AND PSD.PATROL_TYPE <> -1
AND PSD.IS_NEED_PDA = '1'
AND PPWP.PATROL_FLAG = 1
AND PTWS.IS_COMPLETE = '3'
AND TO_CHAR(PTWS.REAL_END_DATE, 'YYYY') = '2013'
AND PTPO.DEVICE_ID = 1003551930) F,
(SELECT COUNT(1) COUNT_RESULT
FROM GG_TASK_WORK_SHEET PTWS,
GG_TASK_PATROL_SHEET_DETAIL PSD,
GG_TASK_PATROL_OBJECT PTPO,
GG_PATROL_EQUIPMENT PPE
WHERE PTWS.WORK_SHEET_ID = PSD.WORK_SHEET_ID
AND PTWS.WORK_SHEET_ID = PTPO.WORK_SHEET_ID
AND PTPO.PATROL_LINE_ID = PPE.PATROL_LINE_ID
AND PTPO.FUNCTION_LOCATION_ID = PPE.FUNCTION_LOCATION_ID
AND PTWS.TASK_TYPE = 4
AND PTWS.SHEET_TYPE = 1
AND PTPO.PATROL_TYPE = 1
AND PSD.PATROL_TYPE = -1
AND PSD.IS_NEED_PDA = '1'
AND PTPO.ARRIVE_TYPE = 1
AND PTWS.IS_COMPLETE = '3'
AND TO_CHAR(PTWS.REAL_END_DATE, 'YYYY') = '2013'
AND PPE.DEVICE_ID = 1003551930) G,
(SELECT COUNT(1) COUNT_RESULT
FROM GG_TASK_WORK_SHEET PTWS,
GG_TASK_PATROL_SHEET_DETAIL PSD,
GG_TASK_PATROL_OBJECT PTPO,
GG_PATROL_EQUIPMENT PPE
WHERE PTWS.WORK_SHEET_ID = PSD.WORK_SHEET_ID
AND PTWS.WORK_SHEET_ID = PTPO.WORK_SHEET_ID
AND PTPO.PATROL_LINE_ID = PPE.PATROL_LINE_ID
AND PTPO.FUNCTION_LOCATION_ID = PPE.FUNCTION_LOCATION_ID
AND PTWS.TASK_TYPE = 4
AND PTWS.SHEET_TYPE = 1
AND PTPO.PATROL_TYPE = 1
AND PSD.PATROL_TYPE <> -1
AND PSD.IS_NEED_PDA = '1'
AND PTPO.ARRIVE_TYPE = 1
AND PTWS.IS_COMPLETE = '3'
AND TO_CHAR(PTWS.REAL_END_DATE, 'YYYY') = '2013'
AND PPE.DEVICE_ID = 1003551930) H) ARRIVED_DEVICE,
(SELECT A.COUNT_RESULT + B.COUNT_RESULT + C.COUNT_RESULT +
D.COUNT_RESULT ALL_COUNT
FROM (SELECT COUNT(1) COUNT_RESULT
FROM GG_TASK_WORK_SHEET PTWS,
GG_TASK_PATROL_SHEET_DETAIL PSD,
GG_PATROL_WORK_POINT PPWP,
GG_PATROL_POINT PPP,
GG_PATROL_EQUIPMENT PPE
WHERE PTWS.WORK_SHEET_ID = PSD.WORK_SHEET_ID
AND TO_CHAR(PTWS.WORK_SHEET_ID) = PPWP.WORK_ID
AND PPWP.PATROL_POINT_ID = PPP.PATROL_POINT_ID
AND PPP.PATROL_POINT_ID = PPE.PATROL_POINT_ID
AND PTWS.TASK_TYPE = 4
AND PTWS.SHEET_TYPE = 2
AND