[SAS课件] 斯坦福大学sas教学课件SAS_SQL1.ppt

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1、IntroductionTheStructuredQueryLanguage(SQL)isastandardizedlanguageusedtoretrieveandupdatedatastoredinrelationaltables(ordatabases).WhencodinginSQL,theuserisnotrequiredtoknowthephysicalattributesofthetablesuchasdatalocationandtype.SQLisnonprocedural.Thepur

2、poseistoallowtheprogrammertofocusonwhatdatashouldbeselectedandnothowtoselectthedata.ThemethodofretrievalisdeterminedbytheSQLoptimizer,notbytheuser.Whatisatable?Atableisatwodimensionalrepresentationofdataconsistingofcolumnsandrows.IntheSQLprocedureatableca

3、nbeaSASdataset,SASdataview,ortablefromaRDBMS.Tablesarelogicallyrelatedbyvaluessuchasakeycolumn.RelationalTablesInSQLtablesarelogicallyrelatedbyakeycolumnorcolumns.SimpleQueriesIwouldliketoselectlastname,department,andsalaryfromtheemployeetablewheretheempl

4、oyee'ssalaryisgreaterthan35,000.Howwouldthisquery(request)lookinSQL?SELECTLASTNAME,DEPARTMENT,SALARYFROMCLASS.EMPLOYWHERESALARYGT35000Aqueryismerelyarequestforinformationfromatableortables.Thequeryresultistypicallyareportbutcanalsobeanothertable.BasicSynt

5、axPROCSQLStatements(clauses)intheSQLprocedurearenotseparatedbysemicolons,theentirequeryisterminatedwithasemicolon.ItemsinanSQLstatementareseparatedbyacomma.Thereisarequiredorderofstatementsinaquery.OneSQLprocedurecancontainmanyqueriesandaquerycanreference

6、theresultsfrompreviousqueries.TheSQLprocedurecanbeterminatedwithaQUITstatement,RUNstatementshavenoeffect.ExampleIwouldliketoselectthesocialsecuritynumber,salaryandbonus(columns)forallemployees(rows)fromtheemployeetableLIBNAMECLASS'C:CYDATA';PROCSQL;SELEC

7、TSSN,SALARY,BONUSFROMCLASS.EMPLOYEE;SelectingRowswithaWHEREClauseExample:Iwouldliketoselectthesocialsecuritynumber,salaryandbonus(columns)fromtheemployeetablewheretheemployeeisindepartmentGIOandhasasalarylessthat35,000.PROCSQL;SELECTSSN,SALARY,BONUSFROMC

8、LASS.EMPLOYEEWHEREDEPT='GIO'ANDSALARYLT35000;QUIT;WHEREClauseOperatorsTheWHEREclausesupportsmanycomparisonoperators.ItalsosupportslogicalNOTsandAND/ORtocreatecompoundexpressions.Standardcomparisonoperators：Specialop