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Oracle Query Optimization

Oracle Database Tips by Donald Burleson


I would like to execute my query faster: can you please help me? The query works but it can get slow with different values... 

select distinct (tb1.SupporterID), tb1.lotteryNumber, tb1.DrawNumber,tb1.PrizeDrawID, tb1.prizeValue, tb1.winningTicket, tb1.title, tb1.initials, tb1.surname, tb1.address1,tb1.address2,tb1.address3,tb1.address4,
tb1.supporterNumber, tb1.prizeName from (select distinct pw1.SupporterID, pw1.PrizeWinID,Lpt.lotteryNumber, pw1.DrawNumber, pw1.PrizeDrawID, pd.prizeValue, pw1.winningTicket, pw1.title, pw1.initials, pw1.surname,pw1.address1,pw1.address2,pw1.address3,
pw1.address4, s.supporterNumber,p.prizeName from prize_win pw1inner join ( select pt.purchasedTicketID,L.lotteryNumber from purchased_Ticket pt inner join lottery L on  pt.lotteryID = L.lotteryID where L.lotteryNumber between 215 and 230) Lpt on pw1.PurchasedTicketID =Lpt.purchasedTicketID inner join prize_draw pd on pw1.PrizeDrawID =pd.PrizeDrawID inner join supporter s on pw1.SupporterID = s.SupporterID inner join prize p on pw1.PrizeDrawID = p.PrizeDrawID) tb1 inner
join (select pw1.SupporterID, pw1.PrizeWinID from prize_win  pw1 inner join (select pt.purchasedTicketID from purchased_Ticket pt inner join lottery L on pt.lotteryID = L.lotteryID where L.lotteryNumber between 215 and 230) Lpt on pw1.PurchasedTicketID = Lpt.purchasedTicketID ) tb2 on tb1.SupporterID = tb2.SupporterID where tb1.PrizeWinID <> tb2.PrizeWinID order by tb1.SupporterID asc;


This question posed on 10 January 2006


Usually when the response time changes based on the values this indicates data skew. In other words, you put in "where x=10" you get back 5 values, "where x=5" gives back 3000. Oracle assumes that data is equally distributed around indexed values. If the data is not equally distributed about an index it is skewed. In order to help the optimizer with skewed data you need to use histograms. Histograms are created using the ANALYZE command or through options in the DBMS_STATS gather procedures.




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