SQL数据库中英文对照外文翻译文献.docx

SQL数据库中英文对照外文翻译文献.docx

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SQL数据库中英文对照外文翻译文献

中英文对照外文翻译文献

（文档含英文原文和中文翻译）

WorkingwithDatabases

ThischapterdescribeshowtouseSQLstatementsinembeddedapplicationstocontroldatabases.Therearethreedatabasestatementsthatsetupandopendatabasesforaccess:

SETDATABASEdeclaresadatabasehandle,associatesthehandlewithanactualdatabasefile,andoptionallyassignsoperationalparametersforthedatabase.

SETNAMESoptionallyspecifiesthecharactersetaclientapplicationusesforCHAR,VARCHAR,andtextBlobdata.Theserverusesthisinformationtotransliteratefromadatabase’sdefaultcharactersettotheclient’scharactersetonSELECToperations,andtotransliteratefromaclientapplication’scharactersettothedatabasecharactersetonINSERTandUPDATEoperations.

gCONNECTopensadatabase,allocatessystemresourcesforit,andoptionallyassignsoperationalparametersforthedatabase.Alldatabasesmustbeclosedbeforeaprogramends.AdatabasecanbeclosedbyusingDISCONNECT,orbyappendingtheRELEASEoptiontothefinalCOMMITorROLLBACKinaprogram.

Declaringadatabase

Beforeadatabasecanbeopenedandusedinaprogram,itmustfirstbedeclaredwithSETDATABASEto:

CHAPTER3WORKINGWITHDATABASES.Establishadatabasehandle.Associatethedatabasehandlewithadatabasefilestoredonalocalorremotenode.Adatabasehandleisaunique,abbreviatedaliasforanactualdatabasename.DatabasehandlesareusedinsubsequentCONNECT,COMMITRELEASE,andROLLBACKRELEASEstatementstospecifywhichdatabasestheyshouldaffect.ExceptindynamicSQL（DSQL）applications,databasehandlescanalsobeusedinsidetransactionblockstoqualify,ordifferentiate,tablenameswhentwoormoreopendatabasescontainidenticallynamedtables.

Eachdatabasehandlemustbeuniqueamongallvariablesusedinaprogram.Databasehandlescannotduplicatehost-languagereservedwords,andcannotbeInterBasereservedwords.Thefollowingstatementillustratesasimpledatabasedeclaration:

EXECSQL

SETDATABASEDB1=’employee.gdb’;

Thisdatabasedeclarationidentifiesthedatabasefile,employee.gdb,asadatabasetheprogramuses,andassignsthedatabaseahandle,oralias,DB1.

Ifaprogramrunsinadirectorydifferentfromthedirectorythatcontainsthedatabasefile,thenthefilenamespecificationinSETDATABASEmustincludeafullpathname,too.Forexample,thefollowingSETDATABASEdeclarationspecifiesthefullpathtoemployee.gdb:

EXECSQL

SETDATABASEDB1=’/interbase/examples/employee.gdb’;

Ifaprogramandadatabasefileitusesresideondifferenthosts,thenthefilenamespecificationmustalsoincludeahostname.ThefollowingdeclarationillustrateshowaUnixhostnameisincludedaspartofthedatabasefilespecificationonaTCP/IPnetwork:

EXECSQL

SETDATABASEDB1=’jupiter:

/usr/interbase/examples/employee.gdb’;

OnaWindowsnetworkthatusestheNetbeuiprotocol,specifythepathasfollows:

EXECSQL

SETDATABASEDB1=’//venus/C:

/Interbase/examples/employee.gdb’;

DECLARINGADATABASE

EMBEDDEDSQLGUIDE37

Declaringmultipledatabases

AnSQLprogram,butnotaDSQLprogram,canaccessmultipledatabasesatthesametime.Inmulti-databaseprograms,databasehandlesarerequired.Ahandleisusedto:

1.Referenceindividualdatabasesinamulti-databasetransaction.

2.Qualifytablenames.

3.SpecifydatabasestoopeninCONNECTstatements.

IndicatedatabasestoclosewithDISCONNECT,COMMITRELEASE,andROLLBACKRELEASE.

DSQLprogramscanaccessonlyasingledatabaseatatime,sodatabasehandleuseisrestrictedtoconnectingtoanddisconnectingfromadatabase.

Inmulti-databaseprograms,eachdatabasemustbedeclaredinaseparateSETDATABASEstatement.Forexample,thefollowingcodecontainstwoSETDATABASEstatements:

...

EXECSQL

SETDATABASEDB2=’employee2.gdb’;

EXECSQL

SETDATABASEDB1=’employee.gdb’;

...

4Usinghandlesfortablenames

Whenthesametablenameoccursinmorethanonesimultaneouslyaccesseddatabase,adatabasehandlemustbeusedtodifferentiateonetablenamefromanother.Thedatabasehandleisusedasaprefixtotablenames,andtakestheformhandle.table.

Forexample,inthefollowingcode,thedatabasehandles,TESTandEMP,areusedtodistinguishbetweentwotables,eachnamedEMPLOYEE:

...

EXECSQL

DECLAREIDMATCHCURSORFOR

SELECTTESTNOINTO:

matchidFROMTEST.EMPLOYEE

WHERETESTNO>100;

EXECSQL

DECLAREEIDMATCHCURSORFOR

SELECTEMPNOINTO:

empidFROMEMP.EMPLOYEE

WHEREEMPNO=:

matchid;

...

CHAPTER3WORKINGWITHDATABASES

38INTERBASE6

IMPORTANT

ThisuseofdatabasehandlesappliesonlytoembeddedSQLapplications.DSQLapplicationscannotaccessmultipledatabasessimultaneously.

4Usinghandleswithoperations

Inmulti-databaseprograms,databasehandlesmustbespecifiedinCONNECTstatementstoidentifywhichdatabasesamongsever