Identity_Insert:UnderstandingOneofSQLServer'sMostUsefulTools
SQLServerisoneofthemostwidelyusedRelationalDatabaseManagementSystems(RDBMS)intheworldandprovidesmanypowerfultoolsfordevelopersanddatabaseadministratorsalike.OnesuchtoolistheIdentity_Insertoption,whichallowsuserstoinsertspecificvaluesintoatable'sidentitycolumn.Inthisarticle,we'llexplorewhattheIdentity_Insertoptiondoes,whyit'simportant,andhowtouseiteffectively.
WhatisIdentity_Insert,andWhyisitImportant?
Bydefault,SQLServerautomaticallygeneratesauniqueidentityvalueforeveryrowaddedtoatable'sidentitycolumn.Thishelpsensurethateachrecordinthetablehasauniqueidentifier,whichcanbeusefulformanypurposessuchasretrieval,maintainingreferentialintegrity,andtrackingchangesovertime.However,theremaybetimeswhenyouneedtoexplicitlyspecifythevalueforanidentitycolumnratherthanrelyingonSQLServertogenerateitforyou.
ThisiswheretheIdentity_Insertoptioncomesin.Byenablingthisoption,youcanmanuallyinsertspecificvaluesintotheidentitycolumnofatable.Thiscanbeparticularlyusefulwhenyouaremigratingdatafromonesystemtoanotherandneedtopreservetheoriginalidentitiesoftherecords.Itcanalsobehelpfulwhenyouneedtomanuallycontroltheorderinwhichrecordsareinsertedorupdated,suchaswhenyouareloadingdataintoafacttableforadatawarehouse.
HowtoUseIdentity_InsertinSQLServer
UsingIdentity_InsertinSQLServerisrelativelysimple,butthereareafewimportantthingstokeepinmind.First,youneedtoensurethatthetableyouwanttoinsertdataintohasanidentitycolumn.Thiscanbespecifiedwhencreatingthetableusingthe'identity'keywordaspartofthecolumndefinition,orbyalteringtheexistingtabletoaddanidentitycolumn.
Onceyouhaveatablewithanidentitycolumn,youcanenabletheIdentity_Insertoptiononthattableusingthefollowingsyntax:
SETIDENTITY_INSERTTableNameON
ThisstatementtellsSQLServerthatyouwanttoinsertspecificvaluesintotheidentitycolumnofthespecifiedtable.OnceyouhaveenabledIdentity_Insert,youcanthenexecuteaninsertstatementspecifyingthevaluesyouwanttousefortheidentitycolumn.Forexample:
INSERTINTOTableName(Id,Name)VALUES(123,'JohnDoe')
Whenyouarefinishedinsertingdata,besuretodisabletheIdentity_Insertoptionusingthefollowingsyntax:
SETIDENTITY_INSERTTableNameOFF
It'salsoworthnotingthattherearesomelimitationstousingIdentity_InsertinSQLServer.Forexample,youcannotenablethisoptionforavieworanindexedview,andyoucannotuseittochangetheidentityvaluesofexistingrows.
Conclusion
TheIdentity_Insertoptionisapowerfultoolthatcanbeextremelyusefulincertainsituations.Whetheryouaremigratingdatabetweensystemsorneedtomanuallycontroltheorderinwhichrecordsareinserted,thisoptioncanhelpensurethatyourdataisaccurateandproperlyidentified.Byfollowingthestepsoutlinedinthisarticle,youcangetstartedusingIdentity_InsertinSQLServerandtakefulladvantageofthisusefulfeature.
