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1、高性能sql查询语句优化（OptimizationofhighperformanceSQLquery）Intheguaranteeofrealizingthebasicfunction,minimizethedatabaseaccesstimes;throughthesearchparameters,reduceaccesstotablesofrows,minimizingtheresultset,soastoreducetheburdenofthenetwork;toseparateoperationtoseparateprocessing,impr
2、ovetheresponsespeedofeachtime;inthedatawindowusingSQL,trytousetheindexsetintheselectionofthefirst;thestructureofthealgorithmisassimpleaspossible;inthequery,notexcessiveuseofwildcardssuchasSELECT*FROMT1statementtouseseveralcolumnswillselectseveralcolumnssuchas:SELECTCOL1,COL2FROM
3、T1;wherepossibletrytolimitthenumberofresultsetrowssuchas:SELECTTOP300COL1.COL2,COL3FROMT1,becauseinsomecasestheuserisnotneededsomuchdata.Intheabsenceofindex,thedatabasetofindacertaindata,youmusthaveafulltablescanning,alldatatraverseonce,findouttheconditionoftherecord.Inthecaseof
4、asmallamountofdata,theremaybenoobviousdifference,butwhentheamountofdataislarge,thissituationisverybad.HowSQLstatementsareexecutedinSQLSERVER,andtheyworrythattheirwrittenSQLstatementswillbemisunderstoodbySQLSERVER.Forexample:Select*fromtable1wherename='Zhangsan'andtID>10000Andexe
5、cute:Select*fromtable1wheretID>10000andname='Zhangsan'Somepeopledonotknowmorethantwostatementexecutionefficiencyisthesame,becauseifasimplestatementhasfromthepointofview,thesetwostatementsarenotthesame,iftIDisapolymerizationindex,thenasimplylookupfrom10000aftertherecordinjustasen
6、tence;tostartfromthewholetabletofindoneofname='Zhangsan',andthenaccordingtotheconstraintconditionstID>10000toputforwardthequeryresults.Infact,suchfearsareunnecessary.ThereisaqueryanalysisoptimizerinSQLSERVER,whichcancalculatethesearchconditionsinthewhereclauseanddeterminewhichin
7、dexcanreducethesearchspaceofthetablescan,thatistosay,itcanrealizeautomaticoptimization.Althoughqueryoptimizercanautomaticallyqueryoptimizationaccordingtothewhereclause,sometimesthequeryoptimizerdoesnotqueryquicklyaccordingtoyouroriginalintention.Inthequeryanalysisphase,thequeryo
8、ptimizerlooksateachphaseofthequeryanddetermines
