structured query language...structured query language (sql) 3.2 create tables using the designer...
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StructuredQueryLanguageHans-PetterHalvorsen
StructuredQueryLanguage
Hans-PetterHalvorsen
Copyright©2017
https://www.halvorsen.blog
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TableofContents1 IntroductiontoSQL...........................................................................................................6
1.1 DataDefinitionLanguage(DDL)..................................................................................8
1.2 DataManipulationLanguage(DML)...........................................................................8
2 IntroductiontoSQLServer................................................................................................9
2.1 SQLServerManagementStudio...............................................................................10
2.1.1 CreateanewDatabase......................................................................................11
2.1.2 Queries..............................................................................................................12
3 CREATETABLE.................................................................................................................13
3.1 DatabaseModelling..................................................................................................15
3.2 CreateTablesusingtheDesignerTools....................................................................17
3.3 SQLConstraints.........................................................................................................17
3.3.1 PRIMARYKEY.....................................................................................................18
3.3.2 FOREIGNKEY.....................................................................................................19
3.3.3 NOTNULL/RequiredColumns.........................................................................22
3.3.4 UNIQUE.............................................................................................................23
3.3.5 CHECK................................................................................................................25
3.3.6 DEFAULT............................................................................................................27
3.3.7 AUTOINCREMENTorIDENTITY.........................................................................28
3.4 ALTERTABLE.............................................................................................................29
4 INSERTINTO....................................................................................................................31
5 UPDATE...........................................................................................................................33
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6 DELETE.............................................................................................................................35
7 SELECT.............................................................................................................................37
7.1 TheORDERBYKeyword............................................................................................39
7.2 SELECTDISTINCT.......................................................................................................40
7.3 TheWHEREClause....................................................................................................40
7.3.1 Operators..........................................................................................................41
7.3.2 LIKEOperator....................................................................................................41
7.3.3 INOperator........................................................................................................42
7.3.4 BETWEENOperator...........................................................................................42
7.4 Wildcards..................................................................................................................42
7.5 AND&OROperators................................................................................................43
7.6 SELECTTOPClause....................................................................................................44
7.7 Alias..........................................................................................................................45
7.8 Joins..........................................................................................................................45
7.8.1 DifferentSQLJOINs...........................................................................................46
8 SQLScripts.......................................................................................................................48
8.1 UsingComments.......................................................................................................48
8.1.1 Single-linecomment..........................................................................................48
8.1.2 Multiple-linecomment......................................................................................48
8.2 Variables...................................................................................................................49
8.3 Built-inGlobalVariables...........................................................................................50
8.3.1 @@IDENTITY.....................................................................................................50
8.4 FlowControl.............................................................................................................51
8.4.1 IF–ELSE.............................................................................................................51
8.4.2 WHILE................................................................................................................52
8.4.3 CASE...................................................................................................................53
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8.4.4 CURSOR.............................................................................................................54
9 Views...............................................................................................................................56
9.1 UsingtheGraphicalDesigner...................................................................................57
10 StoredProcedures........................................................................................................61
10.1 NOCOUNTON/NOCOUNTOFF..............................................................................64
11 Functions......................................................................................................................66
11.1 Built-inFunctions..................................................................................................66
11.1.1 StringFunctions.............................................................................................66
11.1.2 DateandTimeFunctions...............................................................................67
11.1.3 MathematicsandStatisticsFunctions...........................................................67
11.1.4 AVG()..............................................................................................................68
11.1.5 COUNT().........................................................................................................68
11.1.6 TheGROUPBYStatement..............................................................................69
11.1.7 TheHAVINGClause........................................................................................70
11.2 User-definedFunctions.........................................................................................71
12 Triggers.........................................................................................................................72
13 CommunicationfromotherApplications.....................................................................75
13.1 ODBC.....................................................................................................................75
13.2 MicrosoftExcel......................................................................................................76
14 References....................................................................................................................78
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1 IntroductiontoSQLSQL(StructuredQueryLanguage)isadatabasecomputerlanguagedesignedformanagingdatainrelationaldatabasemanagementsystems(RDBMS).
SQL,isastandardizedcomputerlanguagethatwasoriginallydevelopedbyIBMforquerying,alteringanddefiningrelationaldatabases,usingdeclarativestatements.
SQLispronounced/ˌɛskjuːˈɛl/ (letterbyletter) or/ˈsiːkwəl/ (asaword).
WhatcanSQLdo?
• SQLcanexecutequeriesagainstadatabase• SQLcanretrievedatafromadatabase• SQLcaninsertrecordsinadatabase• SQLcanupdaterecordsinadatabase• SQLcandeleterecordsfromadatabase
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• SQLcancreatenewdatabases• SQLcancreatenewtablesinadatabase• SQLcancreatestoredproceduresinadatabase• SQLcancreateviewsinadatabase• SQLcansetpermissionsontables,procedures,andviews
EvenifSQLisastandard,manyofthedatabasesystemsthatexisttodayimplementtheirownversionoftheSQLlanguage.Inthisdocument,wewillusetheMicrosoftSQLServerasanexample.
Therearelotsofdifferentdatabasesystems,orDBMS–DatabaseManagementSystems,suchas:
• MicrosoftSQLServero Enterprise,Developerversions,etc.o Expressversionisfreeofcharge
• Oracle• MySQL(Oracle,previouslySunMicrosystems)-MySQLcanbeusedfreeofcharge
(opensourcelicense),WebsitesthatuseMySQL:YouTube,Wikipedia,Facebook• MicrosoftAccess• IBMDB2• Sybase• …lotsofothersystems
InthisTutorial,wewillfocusonMicrosoftSQLServer.SQLServerusesT-SQL(Transact-SQL).T-SQLisMicrosoft'sproprietaryextensiontoSQL.T-SQLisverysimilartostandardSQL,butinadditionitsupportssomeextrafunctionality,built-infunctions,etc.
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OtherusefulTutorialsaboutdatabases:
• IntroductiontoDatabaseSystems• DatabaseCommunicationinLabVIEW
TheseTutorialsarelocatedat:https://www.halvorsen.blog
1.1 DataDefinitionLanguage(DDL)TheDataDefinitionLanguage(DDL)managestableandindexstructure.ThemostbasicitemsofDDLaretheCREATE,ALTER,RENAMEandDROPstatements:
• CREATEcreatesanobject(atable,forexample)inthedatabase. • DROPdeletesanobjectinthedatabase,usuallyirretrievably. • ALTERmodifiesthestructureanexistingobjectinvariousways—forexample,adding
acolumntoanexistingtable.
1.2 DataManipulationLanguage(DML)TheDataManipulationLanguage(DML)isthesubsetofSQLusedtoadd,updateanddeletedata.
TheacronymCRUDreferstoallofthemajorfunctionsthatneedtobeimplementedinarelationaldatabaseapplicationtoconsideritcomplete.EachletterintheacronymcanbemappedtoastandardSQLstatement:
Operation SQL DescriptionCreate INSERTINTO insertsnewdataintoa
databaseRead(Retrieve) SELECT extractsdatafromadatabaseUpdate UPDATE updatesdatainadatabaseDelete(Destroy) DELETE deletesdatafromadatabase
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2 IntroductiontoSQLServerMicrosoftisthevendorofSQLServer.
WehavedifferenteditionsofSQLServer,whereSQLServerExpressisfreetodownloadanduse.
SQLServerusesT-SQL(Transact-SQL).T-SQLisMicrosoft'sproprietaryextensiontoSQL.T-SQLisverysimilartostandardSQL,butinadditionitsupportssomeextrafunctionality,built-infunctions,etc.T-SQLexpandsontheSQLstandardtoincludeproceduralprogramming,localvariables,varioussupportfunctionsforstringprocessing,dateprocessing,mathematics,etc.
SQLServerconsistsofaDatabaseEngineandaManagementStudio(andlotsofotherstuffwhichwewillnotmentionhere).TheDatabaseenginehasnographicalinterface-itisjustaservicerunninginthebackgroundofyourcomputer(preferableontheserver).TheManagementStudioisgraphicaltoolforconfiguringandviewingtheinformationinthedatabase.Itcanbeinstalledontheserverorontheclient(orboth).
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StructuredQueryLanguage(SQL)
2.1 SQLServerManagementStudioSQLServerManagementStudioisaGUItoolincludedwithSQLServerforconfiguring,managing,andadministeringallcomponentswithinMicrosoftSQLServer.Thetoolincludesbothscripteditorsandgraphicaltoolsthatworkwithobjectsandfeaturesoftheserver.Asmentionedearlier,versionofSQLServerManagementStudioisalsoavailableforSQLServerExpressEdition,forwhichitisknownasSQLServerManagementStudioExpress.
AcentralfeatureofSQLServerManagementStudioistheObjectExplorer,whichallowstheusertobrowse,select,andactuponanyoftheobjectswithintheserver.Itcanbeusedtovisuallyobserveandanalyzequeryplansandoptimizethedatabaseperformance,amongothers.SQLServerManagementStudiocanalsobeusedtocreateanewdatabase,alteranyexistingdatabaseschemabyaddingormodifyingtablesandindexes,oranalyzeperformance.ItincludesthequerywindowswhichprovideaGUIbasedinterfacetowriteandexecutequeries.
WhencreatingSQLcommandsandqueries,the“QueryEditor”(select“NewQuery”fromtheToolbar)isused(showninthefigureabove).
WithSQLandthe“QueryEditor”wecandoalmosteverythingwithcode,butsometimesitisalsoagoodideatousethedifferentDesignertoolsinSQLtohelpusdotheworkwithoutcoding(somuch).
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2.1.1 CreateanewDatabase
ItisquitesimpletocreateanewdatabaseinMicrosoftSQLServer.Justright-clickonthe“Databases”nodeandselect“NewDatabase…”
Therearelotsofsettingsyoumaysetregardingyourdatabase,buttheonlyinformationyoumustfillinisthenameofyourdatabase:
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YoumayalsousetheSQLlanguagetocreateanewdatabase,butsometimesitiseasiertojustusethebuilt-infeaturesintheManagementStudio.
2.1.2 Queries
InordertomakeanewSQLquery,selectthe“NewQuery”buttonfromtheToolbar.
HerewecanwriteanykindofqueriesthatissupportedbytheSQLlanguage.
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3 CREATETABLEBeforeyoustartimplementingyourtablesinthedatabase,youshouldalwaysspendsometimedesignyourtablesproperlyusingadesigntoollike,e.g.,ERwin,ToadDataModeler,PowerDesigner,Visio,etc.ThisiscalledDatabaseModeling.
TheCREATETABLEstatementisusedtocreateatableinadatabase.
Syntax:
CREATE TABLE table_name ( column_name1 data_type, column_name2 data_type, column_name3 data_type, .... )
Thedatatypespecifieswhattypeofdatathecolumncanhold.
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Youhavespecialdatatypesfornumbers,textdates,etc.
Examples:
• Numbers:int,float• Text/Stings:varchar(X)–whereXisthelengthofthestring• Dates:datetime• etc.
Example:
Wewanttocreateatablecalled“CUSTOMER”whichhasthefollowingcolumnsanddatatypes:
CREATE TABLE CUSTOMER ( CustomerId int IDENTITY(1,1) PRIMARY KEY, CustomerNumber int NOT NULL UNIQUE, LastName varchar(50) NOT NULL, FirstName varchar(50) NOT NULL, AreaCode int NULL, Address varchar(50) NULL, Phone varchar(50) NULL, ) GO
Bestpractice:
Whencreatingtablesyoushouldconsiderfollowingtheseguidelines:
• Tables:Useuppercaseandsingularformintablenames–notplural,e.g.,“STUDENT”(notstudents)
• Columns:UsePascalnotation,e.g.,“StudentId”• PrimaryKey:
o Ifthetablenameis“COURSE”,namethePrimaryKeycolumn“CourseId”,etc.
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o “Always”useIntegerandIdentity(1,1)forPrimaryKeys.UseUNIQUEconstraintforothercolumnsthatneedstobeunique,e.g.RoomNumber
• SpecifyRequiredColumns(NOTNULL)–i.e.,whichcolumnsthatneedtohavedataornot
• Standardizeonfew/theseDataTypes:int,float,varchar(x),datetime,bit• UseEnglishfortableandcolumnnames• Avoidabbreviations!(UseRoomNumber–notRoomNo,RoomNr,...)
3.1 DatabaseModellingAsmentioninthebeginningofthechapter,youshouldalwaysstartwithdatabasemodellingbeforeyoustartimplementingthetablesinadatabasesystem.
BelowweseeadatabasemodelincreatedwithERwin.
Withthistoolwecantransferthedatabasemodelastablesintodifferentdatabasesystems,suchase.g.,SQLServer.CAERwinDataModelerCommunityEditionisfreewitha25objectslimit.IthassupportforOracle,SQLServer,MySQL,ODBCandSybase.
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BelowweseethesametablesinsidethedesigntoolinSQLServer.
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3.2 CreateTablesusingtheDesignerToolsEvenifyoucando“everything”usingtheSQLlanguage,itissometimeseasiertodoitinthedesignertoolsintheManagementStudioinSQLServer.
Insteadofcreatingascriptyoumayaswelleasilyusethedesignerforcreatingtables.
Step1:Select“NewTable…”:
Step2:Next,thetabledesignerpopsupwhereyoucanaddcolumns,datatypes,etc.
InthisdesignerwemayalsospecifyColumnNames,DataTypes,etc.
Step3:SavethetablebyclickingtheSavebutton.
3.3 SQLConstraintsConstraintsareusedtolimitthetypeofdatathatcangointoatable.
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Constraintscanbespecifiedwhenatableiscreated(withtheCREATETABLEstatement)orafterthetableiscreated(withtheALTERTABLEstatement).
Herearethemostimportantconstraints:
• PRIMARYKEY• NOTNULL• UNIQUE• FOREIGNKEY• CHECK• DEFAULT• IDENTITY
Inthesectionsbelowwewillexplainsomeoftheseindetail.
3.3.1 PRIMARYKEY
ThePRIMARYKEYconstraintuniquelyidentifieseachrecordinadatabasetable.
Primarykeysmustcontainuniquevalues.Itisnormaltojustuserunningnumbers,like1,2,3,4,5,…asvaluesinPrimaryKeycolumn.ItisagoodideatoletthesystemhandlethisforyoubyspecifyingthatthePrimaryKeyshouldbesettoidentity(1,1).IDENTITY(1,1)meansthefirstvaluewillbe1andthenitwillincrementby1.
Eachtableshouldhaveaprimarykey,andeachtablecanhaveonlyONEprimarykey.
IfwetakeacloserlookattheCUSTOMERtablecreatedearlier:
CREATE TABLE [CUSTOMER] ( CustomerId int IDENTITY(1,1) PRIMARY KEY, CustomerNumber int NOT NULL UNIQUE, LastName varchar(50) NOT NULL, FirstName varchar(50) NOT NULL, AreaCode int NULL, Address varchar(50) NULL, Phone varchar(50) NULL, ) GO
Asyouseeweusethe“PrimaryKey”keywordtospecifythatacolumnshouldbethePrimaryKey.
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SettingPrimaryKeysintheDesignerTools:
IfyouusetheDesignertoolsinSQLServer,youcaneasilysettheprimaryKeyinatablejustbyright-clickandselect“SetprimaryKey”.
TheprimaryKeycolumnwillthenhaveasmallkey infronttoillustratethatthiscolumnisaPrimaryKey.
3.3.2 FOREIGNKEY
AFOREIGNKEYinonetablepointstoaPRIMARYKEYinanothertable.
Example:
WewillcreateaCREATETABLEscriptforthesetables:
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SCHOOL:
CREATE TABLE SCHOOL ( SchoolId int IDENTITY(1,1) PRIMARY KEY, SchoolName varchar(50) NOT NULL UNIQUE, Description varchar(1000) NULL, Address varchar(50) NULL, Phone varchar(50) NULL, PostCode varchar(50) NULL, PostAddress varchar(50) NULL, ) GO
CLASS:
CREATE TABLE CLASS ( ClassId int IDENTITY(1,1) PRIMARY KEY, SchoolId int NOT NULL FOREIGN KEY REFERENCES SCHOOL (SchoolId), ClassName varchar(50) NOT NULL UNIQUE, Description varchar(1000) NULL, ) GO
TheFOREIGNKEYconstraintisusedtopreventactionsthatwoulddestroylinksbetweentables.
TheFOREIGNKEYconstraintalsopreventsthatinvaliddatafrombeinginsertedintotheforeignkeycolumn,becauseithastobeoneofthevaluescontainedinthetableitpointsto.
SettingForeignKeysintheDesignerTools:
Ifyouwanttousethedesigner,right-clickonthecolumnthatyouwanttobetheForeignKeyandselect“Relationships…”:
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Thefollowingwindowpopsup(ForeignKeyRelationships):
Clickonthe“Add”buttonandthenclickonthesmall“…”button.Thenthefollowingwindowpopsup(TablesandColumns):
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HereyouspecifytheprimaryKeyColumninthePrimaryKeytableandtheForeignKeyColumnintheForeignKeytable.
3.3.3 NOTNULL/RequiredColumns
TheNOTNULLconstraintenforcesacolumntoNOTacceptNULLvalues.
TheNOTNULLconstraintenforcesafieldtoalwayscontainavalue.Thismeansthatyoucannotinsertanewrecord,orupdatearecordwithoutaddingavaluetothisfield.
IfwetakeacloserlookattheCUSTOMERtablecreatedearlier:
CREATE TABLE [CUSTOMER] ( CustomerId int IDENTITY(1,1) PRIMARY KEY, CustomerNumber int NOT NULL UNIQUE, LastName varchar(50) NOT NULL, FirstName varchar(50) NOT NULL, AreaCode int NULL, Address varchar(50) NULL, Phone varchar(50) NULL, ) GO
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Weseethat“CustomerNumber”,“LastName”and“FirstName”issetto“NOTNULL”,thismeansthesecolumnsneedstocontaindata.While“AreaCode”,“Address”and“Phone”maybeleftempty,i.e,theydon’tneedtobefilledout.
Note!AprimarykeycolumncannotcontainNULLvalues.
SettingNULL/NOTNULLintheDesignerTools:
IntheTableDesigneryoucaneasilysetwhichcolumnsthatshouldallowNULLornot:
3.3.4 UNIQUE
TheUNIQUEconstraintuniquelyidentifieseachrecordinadatabasetable.TheUNIQUEandPRIMARYKEYconstraintsbothprovideaguaranteeforuniquenessforacolumnorsetofcolumns.
APRIMARYKEYconstraintautomaticallyhasaUNIQUEconstraintdefinedonit.
Note!YoucanhavemanyUNIQUEconstraintspertable,butonlyonePRIMARYKEYconstraintpertable.
IfwetakeacloserlookattheCUSTOMERtablecreatedearlier:
CREATE TABLE [CUSTOMER] ( CustomerId int IDENTITY(1,1) PRIMARY KEY, CustomerNumber int NOT NULL UNIQUE, LastName varchar(50) NOT NULL, FirstName varchar(50) NOT NULL, AreaCode int NULL, Address varchar(50) NULL,
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Phone varchar(50) NULL, ) GO
Weseethatthe“CustomerNumber”issettoUNIQUE,meaningeachcustomermusthaveauniqueCustomerNumber.Example:
SettingUNIQUEintheDesignerTools:
Ifyouwanttousethedesigner,right-clickonthecolumnthatyouwanttobeUNIQUEandselect“Indexes/Keys…”:
Thenclick“Add”andthensetthe“IsUnique”propertyto“Yes”:
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3.3.5 CHECK
TheCHECKconstraintisusedtolimitthevaluerangethatcanbeplacedinacolumn.
IfyoudefineaCHECKconstraintonasinglecolumnitallowsonlycertainvaluesforthiscolumn.
IfyoudefineaCHECKconstraintonatableitcanlimitthevaluesincertaincolumnsbasedonvaluesinothercolumnsintherow.
Example:
CREATE TABLE [CUSTOMER] ( CustomerId int IDENTITY(1,1) PRIMARY KEY, CustomerNumber int NOT NULL UNIQUE CHECK(CustomerNumber>0), LastName varchar(50) NOT NULL, FirstName varchar(50) NOT NULL, AreaCode int NULL, Address varchar(50) NULL, Phone varchar(50) NULL, ) GO
Inthiscase,whenwetrytoinsertaCustomerNumberlessthanzerowewillgetanerrormessage.
SettingCHECKconstraintsintheDesignerTools:
Ifyouwanttousethedesigner,right-clickonthecolumnwhereyouwanttosettheconstraintsandselect“CheckConstraints…”:
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Thenclick“Add”andthenclick“…”inordertoopentheExpressionwindow:
IntheExpressionwindowyoucantypeintheexpressionyouwanttouse:
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3.3.6 DEFAULT
TheDEFAULTconstraintisusedtoinsertadefaultvalueintoacolumn.
Thedefaultvaluewillbeaddedtoallnewrecords,ifnoothervalueisspecified.
Example:
CREATE TABLE [CUSTOMER] ( CustomerId int IDENTITY(1,1) PRIMARY KEY, CustomerNumber int NOT NULL UNIQUE, LastName varchar(50) NOT NULL, FirstName varchar(50) NOT NULL, Country varchar(20) DEFAULT 'Norway',
AreaCode int NULL, Address varchar(50) NULL, Phone varchar(50) NULL, ) GO
SettingDEFAULTvaluesintheDesignerTools:
Selectthecolumnandgointothe“ColumnProperties”:
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3.3.7 AUTOINCREMENTorIDENTITY
Veryoftenwewouldlikethevalueoftheprimarykeyfieldtobecreatedautomaticallyeverytimeanewrecordisinserted.
Example:
CREATE TABLE CUSTOMER ( CustomerId int IDENTITY(1,1) PRIMARY KEY, CustomerNumber int NOT NULL UNIQUE, LastName varchar(50) NOT NULL, FirstName varchar(50) NOT NULL, AreaCode int NULL, Address varchar(50) NULL, Phone varchar(50) NULL, ) GO
Asshownbelow,weusetheIDENTITY()forthis.IDENTITY(1,1)meansthefirstvaluewillbe1andthenitwillincrementby1.
Settingidentity(1,1)intheDesignerTools:
WecanusethedesignertoolstospecifythataPrimaryKeyshouldbeanidentitycolumnthatisautomaticallygeneratedbythesystemwhenweinsertdataintothetable.
ClickonthecolumninthedesignerandgointotheColumnPropertieswindow:
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3.4 ALTERTABLETheALTERTABLEstatementisusedtoadd,delete,ormodifycolumnsinanexistingtable.
Toaddacolumninatable,usethefollowingsyntax:
ALTER TABLE table_name ADD column_name datatype
Todeleteacolumninatable,usethefollowingsyntax(noticethatsomedatabasesystemsdon'tallowdeletingacolumn):
ALTER TABLE table_name DROP COLUMN column_name
Tochangethedatatypeofacolumninatable,usethefollowingsyntax:
ALTER TABLE table_name ALTER COLUMN column_name datatype
IfweuseCREATETABLEandthetablealreadyexistsinthetablewewillgetanerrormessage,soifwecombineCREATETABLEandALTERTABLEwecancreaterobustdatabasescriptsthatgivesnoerrors,astheexampleshownbelow:
if not exists (select * from dbo.sysobjects where id = object_id(N'[CUSTOMER]') and OBJECTPROPERTY(id, N'IsUserTable') = 1) CREATE TABLE CUSTOMER ( CustomerId int PRIMARY KEY, CustomerNumber int NOT NULL UNIQUE, LastName varchar(50) NOT NULL, FirstName varchar(50) NOT NULL, AreaCode int NULL, Address varchar(50) NULL, Phone varchar(50) NULL, ) GO if exists(select * from dbo.syscolumns where id = object_id(N'[CUSTOMER]') and OBJECTPROPERTY(id, N'IsUserTable') = 1 and name = 'CustomerId') ALTER TABLE CUSTOMER ALTER COLUMN CustomerId int Else ALTER TABLE CUSTOMER ADD CustomerId int GO if exists(select * from dbo.syscolumns where id = object_id(N'[CUSTOMER]') and OBJECTPROPERTY(id, N'IsUserTable') = 1 and name = 'CustomerNumber') ALTER TABLE CUSTOMER ALTER COLUMN CustomerNumber int
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Else ALTER TABLE CUSTOMER ADD CustomerNumber int GO ...
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4 INSERTINTOTheINSERTINTOstatementisusedtoinsertanewrowinatable.
ItispossibletowritetheINSERTINTOstatementintwoforms.
Thefirstformdoesn'tspecifythecolumnnameswherethedatawillbeinserted,onlytheirvalues:
INSERT INTO table_name VALUES (value1, value2, value3,...)
Example:
INSERT INTO CUSTOMER VALUES ('1000', 'Smith', 'John', 12, 'California', '11111111')
Thesecondformspecifiesboththecolumnnamesandthevaluestobeinserted:
INSERT INTO table_name (column1, column2, column3,...) VALUES (value1, value2, value3,...)
Thisformisrecommended!
Example:
INSERT INTO CUSTOMER (CustomerNumber, LastName, FirstName, AreaCode, Address, Phone) VALUES ('1000', 'Smith', 'John', 12, 'California', '11111111')
InsertDataOnlyinSpecifiedColumns:
Itisalsopossibletoonlyadddatainspecificcolumns.
Example:
INSERT INTO CUSTOMER (CustomerNumber, LastName, FirstName) VALUES ('1000', 'Smith', 'John')
Note!YouneedatleasttoincludeallcolumnsthatcannotbeNULL.
WerememberthetabledefinitionfortheCUSTOMERtable:
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i.e.,weneedtoincludeatleast“CustomerNumber”,“LastName”and“FirstName”.“CustomerId”issetto“identity(1,1)”andthereforevaluesforthiscolumnaregeneratedbythesystem.
InsertDataintheDesignerTools:
Whenyouhavecreatedthetables,youcaneasilyinsertdataintothemusingthedesignertools.Right-clickonthespecifictableandselect“EditTop200Rows”:
Thenyoucanenterdatainatableformat,similarto,e.g.,MSExcel:
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5 UPDATETheUPDATEstatementisusedtoupdateexistingrecordsinatable.
Thesyntaxisasfollows:
UPDATE table_name SET column1=value, column2=value2,... WHERE some_column=some_value
Note!NoticetheWHEREclauseintheUPDATEsyntax.TheWHEREclausespecifieswhichrecordorrecordsthatshouldbeupdated.IfyouomittheWHEREclause,allrecordswillbeupdated!
Example:
update CUSTOMER set AreaCode=46 where CustomerId=2
Beforeupdate:
Afterupdate:
Ifyoudon’tincludetheWHEREclausetheresultbecomes:
→SomakesuretoincludetheWHEREclausewhenusingtheUPDATEcommand!
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UpdateDataintheDesignerTools:
Thesamewayyouinsertdatayoucanalsoupdatethedata.Right-clickonthespecifictableandselect“EditTop200Rows”:
Thenyoucanchangeyourdata:
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6 DELETETheDELETEstatementisusedtodeleterowsinatable.
Syntax:
DELETE FROM table_name WHERE some_column=some_value
Note!NoticetheWHEREclauseintheDELETEsyntax.TheWHEREclausespecifieswhichrecordorrecordsthatshouldbedeleted.IfyouomittheWHEREclause,allrecordswillbedeleted!
Example:
delete from CUSTOMER where CustomerId=2
Beforedelete:
Afterdelete:
DeleteAllRows:
Itispossibletodeleteallrowsinatablewithoutdeletingthetable.Thismeansthatthetablestructure,attributes,andindexeswillbeintact:
DELETE FROM table_name
Note!Makesuretodothisonlywhenyoureallymeanit!YoucannotUNDOthisstatement!
DeleteDataintheDesignerTools:
Youdeletedatainthedesignerbyright-clickontherowandselect“Delete”:
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7 SELECTTheSELECTstatementisprobablythemostusedSQLcommand.TheSELECTstatementisusedforretrievingrowsfromthedatabaseandenablestheselectionofoneormanyrowsorcolumnsfromoneormanytablesinthedatabase.
WewillusetheCUSTOMERtableasanexample.
TheCUSTOMERtablehasthefollowingcolumns:
TheCUSTOMERtablecontainsthefollowingdata:
Example:
select * from CUSTOMER
ThissimpleexamplegetsallthedatainthetableCUSTOMER.Thesymbol“*”isusedwhenyouwanttogetallthecolumnsinthetable.
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Ifyouonlywantafewcolumns,youmayspecifythenamesofthecolumnsyouwanttoretrieve,example:
select CustomerId, LastName, FirstName from CUSTOMER
SointhesimplestformwecanusetheSELECTstatementasfollows:
select <column_names> from <table_names>
Ifwewantallcolumns,weusethesymbol“*”
Note!SQLisnotcasesensitive.SELECTisthesameasselect.
ThefullsyntaxoftheSELECTstatementiscomplex,butthemainclausescanbesummarizedas:
SELECT [ ALL | DISTINCT ] [TOP ( expression ) [PERCENT] [ WITH TIES ] ] select_list [ INTO new_table ] [ FROM table_source ] [ WHERE search_condition ] [ GROUP BY group_by_expression ] [ HAVING search_condition ] [ ORDER BY order_expression [ ASC | DESC ] ]
Itseemscomplex,butwewilltakethedifferentpartsstepbystepinthenextsections.
SelectDataintheDesignerTools:
Right-clickonatableandselect“SelectTop1000Rows”:
Thefollowingwillappear:
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ASelectqueryisautomaticallycreatedforyouwhichyoucaneditifyouwantto.
7.1 TheORDERBYKeywordIfyouwantthedatatoappearinaspecificorderyouneedtousethe“orderby”keyword.
Example:
select * from CUSTOMER order by LastName
Youmayalsosortbyseveralcolumns,e.g.likethis:
select * from CUSTOMER order by Address, LastName
Ifyouusethe“orderby”keyword,thedefaultorderisascending(“asc”).Ifyouwanttheordertobeopposite,i.e.,descending,thenyouneedtousethe“desc”keyword.
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select * from CUSTOMER order by LastName desc
7.2 SELECTDISTINCTInatable,someofthecolumnsmaycontainduplicatevalues.Thisisnotaproblem,however,sometimesyouwillwanttolistonlythedifferent(distinct)valuesinatable.
TheDISTINCTkeywordcanbeusedtoreturnonlydistinct(different)values.
Thesyntaxisasfollows:
select distinct <column_names> from <table_names>
Example:
select distinct FirstName from CUSTOMER
7.3 TheWHEREClauseTheWHEREclauseisusedtoextractonlythoserecordsthatfulfillaspecifiedcriterion.
Thesyntaxisasfollows:
select <column_names> from <table_name> where <column_name> operator value
Example:
select * from CUSTOMER where CustomerNumber='1001'
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Note!SQLusessinglequotesaroundtextvalues,asshownintheexampleabove.
7.3.1 Operators
WiththeWHEREclause,thefollowingoperatorscanbeused:
Operator Description= Equal<> Notequal > Greaterthan < Lessthan >= Greaterthanorequal <= Lessthanorequal BETWEEN Betweenaninclusiverange LIKE Searchforapattern IN Ifyouknowtheexactvalueyouwanttoreturnforatleastoneofthe
columns
Examples:
select * from CUSTOMER where AreaCode>30
7.3.2 LIKEOperator
TheLIKEoperatorisusedtosearchforaspecifiedpatterninacolumn.
Syntax:
SELECT column_name(s) FROM table_name WHERE column_name LIKE pattern
Example:
select * from CUSTOMER where LastName like 'J%'
Note!The"%"signcanbeusedtodefinewildcards(missinglettersinthepattern)bothbeforeandafterthepattern.
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select * from CUSTOMER where LastName like '%a%'
YoumayalsocombinewiththeNOTkeyword,example:
select * from CUSTOMER where LastName not like '%a%'
7.3.3 INOperator
TheINoperatorallowsyoutospecifymultiplevaluesinaWHEREclause.
Syntax:
SELECT column_name(s) FROM table_name WHERE column_name IN (value1,value2,...)
7.3.4 BETWEENOperator
TheBETWEENoperatorselectsarangeofdatabetweentwovalues.Thevaluescanbenumbers,text,ordates.
Syntax:
SELECT column_name(s) FROM table_name WHERE column_name BETWEEN value1 AND value2
7.4 WildcardsSQLwildcardscansubstituteforoneormorecharacterswhensearchingfordatainadatabase.
Note!SQLwildcardsmustbeusedwiththeSQLLIKEoperator.
WithSQL,thefollowingwildcardscanbeused:
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Wildcard Description% Asubstituteforzeroormorecharacters_ Asubstituteforexactlyonecharacter[charlist] Anysinglecharacterincharlist[^charlist]or[!charlist]
Anysinglecharacternotincharlist
Examples:
SELECT * FROM CUSTOMER WHERE LastName LIKE 'J_cks_n'
SELECT * FROM CUSTOMER WHERE CustomerNumber LIKE '[10]%'
7.5 AND&OROperatorsTheANDoperatordisplaysarecordifboththefirstconditionandthesecondconditionistrue.
TheORoperatordisplaysarecordifeitherthefirstconditionorthesecondconditionistrue.
Examples:
select * from CUSTOMER where LastName='Smith' and FirstName='John'
select * from CUSTOMER where LastName='Smith' or FirstName='John'
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CombiningAND&OR:
YoucanalsocombineANDandOR(useparenthesistoformcomplexexpressions).
Example:
select * from CUSTOMER where LastName='Smith' and (FirstName='John' or FirstName='Smith')
7.6 SELECTTOPClauseTheTOPclauseisusedtospecifythenumberofrecordstoreturn.
TheTOPclausecanbeveryusefulonlargetableswiththousandsofrecords.Returningalargenumberofrecordscanimpactonperformance.
Syntax:
SELECT TOP number|percent column_name(s) FROM table_name
Examples:
select TOP 1 * from CUSTOMER
Youcanalsospecifyinpercent:
select TOP 60 percent * from CUSTOMER
Thisisveryusefulforlargetableswiththousandsofrecords
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7.7 AliasYoucangiveatableoracolumnanothernamebyusinganalias.Thiscanbeagoodthingtodoifyouhaveverylongorcomplextablenamesorcolumnnames.
Analiasnamecouldbeanything,butusuallyitisshort.
SQLAliasSyntaxforTables:
SELECT column_name(s) FROM table_name AS alias_name
SQLAliasSyntaxforColumns:
SELECT column_name AS alias_name FROM table_name
7.8 JoinsSQLjoinsareusedtoquerydatafromtwoormoretables,basedonarelationshipbetweencertaincolumnsinthesetables.
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7.8.1 DifferentSQLJOINs
Beforewecontinuewithexamples,wewilllistthetypesofJOINyoucanuse,andthedifferencesbetweenthem.
• JOIN:Returnrowswhenthereisatleastonematchinbothtables• LEFTJOIN:Returnallrowsfromthelefttable,eveniftherearenomatchesinthe
righttable• RIGHTJOIN:Returnallrowsfromtherighttable,eveniftherearenomatchesinthe
lefttable• FULLJOIN:Returnrowswhenthereisamatchinoneofthetables
Example:
Given2tables:
• SCHOOL• CLASS
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Thediagramisshownbelow:
Wewanttogetthefollowinginformationusingaquery:
SchoolName ClassName
… …
… …
InordertogetinformationfrommorethanonetableweneedtousetheJOIN.TheJOINisusedtojointheprimarykeyinonetablewiththeforeignkeyinanothertable.
select SCHOOL.SchoolName, CLASS.ClassName from SCHOOL INNER JOIN CLASS ON SCHOOL.SchoolId = CLASS.SchoolId
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8 SQLScriptsASQLscriptisacollectionofSQLstatementsthatyoucanexecuteinoneoperation.YoucanuseanykindofSQLcommands,suchasinsert,select,delete,update,etc.Inadditionyoucandefineandusevariables,andyoumayalsouseprogramflowlikeIf-Else,etc.Youmayalsoaddcommentstomakethescripteasiertoreadandunderstand.
8.1 UsingCommentsUsingcommentsinyouSQLscriptisimportanttomakethescripteasiertoreadandunderstand.
InSQLwecanuse2differentkindsofcomments:
• Single-linecomment• Multiple-linecomment
8.1.1 Single-linecomment
Wecancommentonelineatthetimeusing“--”beforethetextyouwanttocommentout.
Syntax:
-- text_of_comment
8.1.2 Multiple-linecomment
Wecancommentseverallineusing“/*”inthestartofthecommentand“*/”intheendofthecomment.
Syntax:
/* text_of_comment text_of_comment */
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8.2 VariablesTheabilitytousingvariablesinSQLisapowerfulfeature.YouneedtousethekeywordDECLAREwhenyouwanttodefinethevariables.Localvariablesmusthavethethesymbol“@”asaprefix.Youalsoneedtospecifyadatatypeforyourvariable(int,varchar(x),etc.).
Syntaxfordeclaringvariables:
declare @local_variable data_type
Ifyouhavemorethanonevariableyouwanttodeclare:
declare @myvariable1 data_type, @myvariable2 data_type, …
Whenyouwanttoassignvaluestothevariable,youmustuseeitheraSEToraSELECTstatement.
Example:
declare @myvariable int set @myvariable=4
Ifyouwanttoseethevalueforavariable,youcane.g.,usethePRINTcommandlikethis:
declare @myvariable int set @myvariable=4 print @myvariable
ThefollowingwillbeshowninSQLServer:
AssigningvariableswithavaluefromaSELECTstatementisveryuseful.
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WeusetheCUSTOMERtableasanexample:
Youcanassignavaluetothevariablefromaselectstatementlikethis:
declare @mylastname varchar(50) select @mylastname=LastName from CUSTOMER where CustomerId=2 print @mylastname
YoucanalsouseavariableintheWHEREclauseLIKE,e.g.,this:
declare @find varchar(30) set @find = 'J%' select * from CUSTOMER where LastName LIKE @find
8.3 Built-inGlobalVariablesSQLhavelotsofbuilt-invariablesthatareveryusefultouseinqueriesandscripts.
8.3.1 @@IDENTITY
AfteranINSERT,SELECTINTO,orbulkcopystatementiscompleted,@@IDENTITYcontainsthelastidentityvaluethatisgeneratedbythestatement.Ifthestatementdidnotaffectanytableswithidentitycolumns,@@IDENTITYreturnsNULL.Ifmultiplerowsareinserted,generatingmultipleidentityvalues,@@IDENTITYreturnsthelastidentityvaluegenerated.
Example:
Giventotables;SCHOOLandCOURSE:
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SCHOOLtable: COURSEtable:
WewanttoinsertanewSchoolintotheSCHOOLtableandwewanttoinsert2newCoursesintheCOURSEtablethatbelongtotheSchoolweinsert.Tofindthe“SchoolId”wecanusethe@@IDENTITYvariable:
declare @SchoolId int -- Insert Data into SCHOOL table insert into SCHOOL(SchoolName) values ('MIT') select @SchoolId = @@IDENTITY -- Insert Courses for the specific School above in the COURSE table insert into COURSE(SchoolId,CourseName) values (@SchoolId, 'MIT-101') insert into COURSE(SchoolId,CourseName) values (@SchoolId, 'MIT-201')
Theresultbecomes:
SCHOOLtable: COURSEtable:
8.4 FlowControlAswithotherprogramminglanguagesyoucanusedifferentkindofflowcontrol,suchasIF-ELSE,WHILE,etc,whichisveryuseful.
8.4.1 IF–ELSE
TheIF-ELSEisveryuseful.Belowweseeanexample:
declare @customerNumber int
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select @customerNumber=CustomerNumber from CUSTOMER where CustomerId=2 if @customerNumber > 1000 print 'The Customer Number is larger than 1000' else print 'The Customer Number is not larger than 1000'
BEGIN…END:
IfmorethanonelineofcodeistobeexecutedwithinanIFsentenceyouneedtouseBEGIN…END.
Example:
select @customerNumber=CustomerNumber from CUSTOMER where CustomerId=2 if @customerNumber > 1000 begin print 'The Customer Number is larger than 1000' update CUSTOMER set AreaCode=46 where CustomerId=2 end else print 'The Customer Number is not larger than 1000'
8.4.2 WHILE
WecanalsouseWHILE,whichisknownfromotherprogramminglanguages.
Example:
WeareusingtheCUSTOMERtable:
andthefollowingquery:
while (select AreaCode from CUSTOMER where CustomerId=1) < 20 begin update CUSTOMER set AreaCode = AreaCode + 1
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end select * from CUSTOMER
AsyoucanseethecodeinsidetheWHILEloopisexecutedaslongas“AreaCode”forCustomerId=1islessthan20.Foreachiterationisthe“AreaCode”forthatcustomerincrementedwith1.
8.4.3 CASE
TheCASEstatementevaluatesalistofconditionsandreturnsoneofmultiplepossibleresultexpressions.
Example:
Wehavea“GRADE”tablethatcontainsthegradesforeachstudentindifferentcourses:
select GradeId, StudentId, CourseId, Grade from GRADE
Inthe“GRADE”tableisthegradesstoredasnumbers,butsincethestudentsgetgradeswiththelettersA..F(A=5,B=4,C=3,D=2,E=1,F=0),wewanttoconvertthevaluesinthetableintolettersusingaCASEstatement:
select GradeId, StudentId, CourseId, case Grade when 5 then 'A' when 4 then 'B' when 3 then 'C' when 2 then 'D' when 1 then 'E' when 0 then 'F'
else '-' end as Grade from
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GRADE
8.4.4 CURSOR
Inadvancesscripts,CURSORsmaybeveryuseful.ACURSORworkslikeanadvancedWHILEloopwhichweusetoiteratethroughtherecordsinoneormoretables.
CURSORSareusedmainlyinstoredprocedures,triggers,andSQLscripts.
Example:
WeusetheCUSTOMERtableasanexample:
WewillcreateaCURSORthatiteratethroughalltherecordsintheCUSTOMERtableandcheckifthePhonenumberconsistsof8digits,ifnotthescriptwillreplacetheinvalidPhonenumberwiththetext“Phonenumberisnotvalid”.
HereistheSQLScriptusingaCURSOR:
DECLARE @CustomerId int, @phone varchar(50) DECLARE db_cursor CURSOR FOR SELECT CustomerId from CUSTOMER OPEN db_cursor FETCH NEXT FROM db_cursor INTO @CustomerId WHILE @@FETCH_STATUS = 0 BEGIN select @phone=Phone from CUSTOMER where CustomerId=@CustomerId if LEN(@phone) < 8
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update CUSTOMER set Phone='Phone number is not valid' where CustomerId=@CustomerId FETCH NEXT FROM db_cursor INTO @CustomerId END CLOSE db_cursor DEALLOCATE db_cursor
TheCUSTOMERtablebecomes:
CreatingandusingaCURSORincludesthesesteps:
• DeclareSQLvariablestocontainthedatareturnedbythecursor.Declareonevariableforeachresultsetcolumn.
• AssociateaSQLcursorwithaSELECTstatementusingtheDECLARECURSORstatement.TheDECLARECURSORstatementalsodefinesthecharacteristicsofthecursor,suchasthecursornameandwhetherthecursorisread-onlyorforward-only.
• UsetheOPENstatementtoexecutetheSELECTstatementandpopulatethecursor.• UsetheFETCHINTOstatementtofetchindividualrowsandhavethedataforeach
columnmovedintoaspecifiedvariable.OtherSQLstatementscanthenreferencethosevariablestoaccessthefetcheddatavalues.
• Whenyouarefinishedwiththecursor,usetheCLOSEstatement.Closingacursorfreessomeresources,suchasthecursor'sresultsetanditslocksonthecurrentrow.TheDEALLOCATEstatementcompletelyfreesallresourcesallocatedtothecursor,includingthecursorname.
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9 ViewsViewsarevirtualtableforeasieraccesstodatastoredinmultipletables.
SyntaxforcreatingaView:
CREATE VIEW <ViewName> AS …
...butitmightbeeasiertodoitinthegraphicalviewdesignerthatarebuiltintoSQLManagementStudio.
SyntaxforusingaView:
select * from <MyView> where …
Asshownabove,weuseaVIEWjustlikeweuseanordinarytable.
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Example:
WeusetheSCHOOLandCLASStablesasanexampleforourView.WewanttocreateaViewthatlistsalltheexistingschoolsandthebelongingclasses.
WecreatetheVIEWusingtheCREATEVIEWcommand:
CREATE VIEW SchoolView AS SELECT SCHOOL.SchoolName, CLASS.ClassName FROM SCHOOL INNER JOIN CLASS ON SCHOOL.SchoolId = CLASS.SchoolId
Note!Inordertogetinformationfrommorethanonetable,weneedtolinkthetablestogetherusingaJOIN.
9.1 UsingtheGraphicalDesignerWecreatethesameViewusingthegraphicaldesignerinSQLServerManagementStudio:
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Step1:Right-clickontheViewnodeandselect“NewView…”:
Step2:Addnecessarytables:
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Step3:AddColumns,etc.
Step4:SavetheVIEW:
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Step5:UsetheVIEWinaquery:
select * from SchoolView
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10 StoredProceduresAStoredProcedureisaprecompiledcollectionofSQLstatements.Inastoredprocedureyoucanuseifsentence,declarevariables,etc.
SyntaxforcreatingaStoredProcedure:
CREATE PROCEDURE <ProcedureName> @<Parameter1> <datatype> … declare @myVariable <datatype> … Create your Code here
Note!Youneedtousethesymbol“@”beforevariablenames.
SyntaxforusingaStoredProcedure:
EXECUTE <ProcedureName(…)>
Example:
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WeusetheSCHOOLandCLASStablesasanexampleforourStoredProcedure.WewanttocreateaStoredProcedurethatlistsalltheexistingschoolsandthebelongingclasses.
WecreatetheStoredProcedureasfollows:
CREATE PROCEDURE GetAllSchoolClasses AS select SCHOOL.SchoolName, CLASS.ClassName from SCHOOL inner join CLASS on SCHOOL.SchoolId = CLASS.SchoolId order by SchoolName, ClassName
WhenwehavecreatedtheStoredProcedurewecanrun(orexecute)theStoredprocedureusingtheexecutecommandlikethis:
execute GetAllSchoolClasses
WecanalsocreateaStoreProcedurewithinputparameters.
Example:
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Weusethesametablesinthisexample(SCHOOLandCLASS)butnowwewanttolistallclassesforaspecificschool.
TheStoredProcedurebecomes:
CREATE PROCEDURE GetSpecificSchoolClasses @SchoolName varchar(50) AS select SCHOOL.SchoolName, CLASS.ClassName from SCHOOL inner join CLASS on SCHOOL.SchoolId = CLASS.SchoolId where SchoolName=@SchoolName order by ClassName
Werun(orexecute)theStoredProcedure:
execute GetSpecificSchoolClasses 'TUC'
or:
execute GetSpecificSchoolClasses 'NTNU'
WhenwetrytocreateaStoredProcedurethatalreadyexistswegetthefollowingerrormessage:
There is already an object named 'GetSpecificSchoolClasses' in the database.
Thenwefirstneedtodelete(orDROP)theoldStoredProcedurebeforewecanrecreateitagain.
WecandothismanuallyintheManagementStudioinSQLlikethis:
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Abettersolutionistoaddcodeforthisinourscript,likethis:
IF EXISTS (SELECT name FROM sysobjects WHERE name = GetSpecificSchoolClasses ' AND type = 'P') DROP PROCEDURE GetSpecificSchoolClasses GO CREATE PROCEDURE GetSpecificSchoolClasses @SchoolName varchar(50) AS select SCHOOL.SchoolName, CLASS.ClassName from SCHOOL inner join CLASS on SCHOOL.SchoolId = CLASS.SchoolId where SchoolName=@SchoolName order by ClassName
SoweuseCREATEPROCEDUREtocreateaStoredProcedureandweuseDROPPROCEDUREtodeleteaStoredProcedure.
10.1 NOCOUNTON/NOCOUNTOFFInadvancedStoredProceduresandScript,performanceisveryimportant.UsingSETNOCOUNTONandSETNOCOUNTOFFmakestheStoredProcedurerunfaster.
SETNOCOUNTONstopsthemessagethatshowsthecountofthenumberofrowsaffectedbyaTransact-SQLstatementorstoredprocedurefrombeingreturnedaspartoftheresultset.
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SETNOCOUNTONpreventsthesendingofDONE_IN_PROCmessagestotheclientforeachstatementinastoredprocedure.Forstoredproceduresthatcontainseveralstatementsthatdonotreturnmuchactualdata,orforproceduresthatcontainTransact-SQLloops,settingSETNOCOUNTtoONcanprovideasignificantperformanceboost,becausenetworktrafficisgreatlyreduced.
Example:
IF EXISTS (SELECT name FROM sysobjects WHERE name = 'sp_LIMS_IMPORT_REAGENT' AND type = 'P') DROP PROCEDURE sp_LIMS_IMPORT_REAGENT GO CREATE PROCEDURE sp_LIMS_IMPORT_REAGENT @Name varchar(100), @LotNumber varchar(100), @ProductNumber varchar(100), @Manufacturer varchar(100) AS SET NOCOUNT ON if not exists (SELECT ReagentId FROM LIMS_REAGENTS WHERE [Name]=@Name) INSERT INTO LIMS_REAGENTS ([Name], ProductNumber, Manufacturer) VALUES (@Name, @ProductNumber, @Manufacturer) else UPDATE LIMS_REAGENTS SET [Name] = @Name, ProductNumber = @ProductNumber, Manufacturer = @Manufacturer, WHERE [Name] = @Name SET NOCOUNT OFF GO
ThisStoredProcedureupdatesatableinthedatabaseandinthiscaseyoudon’tnormallyneedfeedback,spsettingSETNOCOUNTONatthetopinthestoredprocedureisagoodidea.itisalsogoodpracticetoSETNOCOUNTOFFatthebottomofthestoredprocedure.
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11 FunctionsWithSQLandSQLServeryoucanuselotsofbuilt-infunctionsoryoumaycreateyourownfunctions.Herewewilllearntousesomeofthemostusedbuilt-infunctionsandinadditionwewillcreateourownfunction.
11.1 Built-inFunctionsSQLhasmanybuilt-infunctionsforperformingcalculationsondata.
Wehave2categoriesoffunctions,namelyaggregatefunctionsandscalarfunctions.Aggregatefunctionsreturnasinglevalue,calculatedfromvaluesinacolumn,whilescalarfunctionsreturnasinglevalue,basedontheinputvalue.
Aggregatefunctions-examples:
• AVG()-Returnstheaveragevalue• STDEV()-Returnsthestandarddeviationvalue• COUNT()-Returnsthenumberofrows• MAX()-Returnsthelargestvalue• MIN()-Returnsthesmallestvalue• SUM()-Returnsthesum• etc.
Scalarfunctions-examples:
• UPPER()-Convertsafieldtouppercase• LOWER()-Convertsafieldtolowercase• LEN()-Returnsthelengthofatextfield• ROUND()-Roundsanumericfieldtothenumberofdecimalsspecified• GETDATE()-Returnsthecurrentsystemdateandtime• etc.
11.1.1 StringFunctions
HerearesomeusefulfunctionsusedtomanipulatewithstringsinSQLServer:
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• CHAR • CHARINDEX • REPLACE • SUBSTRING • LEN • REVERSE • LEFT• RIGHT • LOWER • UPPER • LTRIM • RTRIM
ReadmoreaboutthesefunctionsintheSQLServerHelp.
11.1.2 DateandTimeFunctions
HerearesomeusefulDateandTimefunctionsinSQLServer:
• DATEPART• GETDATE• DATEADD• DATEDIFF• DAY• MONTH• YEAR• ISDATE
ReadmoreaboutthesefunctionsintheSQLServerHelp.
11.1.3 MathematicsandStatisticsFunctions
HerearesomeusefulfunctionsformathematicsandstatisticsinSQLServer:
• COUNT• MIN,MAX• COS,SIN,TAN• SQRT• STDEV• MEAN• AVG
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ReadmoreaboutthesefunctionsintheSQLServerHelp.
11.1.4 AVG()
TheAVG()functionreturnstheaveragevalueofanumericcolumn.
Syntax:
SELECT AVG(column_name) FROM table_name
Example:
GivenaGRADEtable:
Wewanttofindtheaveragegradeforaspecificstudent:
select AVG(Grade) as AvgGrade from GRADE where StudentId=1
11.1.5 COUNT()
TheCOUNT()functionreturnsthenumberofrowsthatmatchesaspecifiedcriteria.
TheCOUNT(column_name)functionreturnsthenumberofvalues(NULLvalueswillnotbecounted)ofthespecifiedcolumn:
SELECT COUNT(column_name) FROM table_name
TheCOUNT(*)functionreturnsthenumberofrecordsinatable:
SELECT COUNT(*) FROM table_name
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WeusetheCUSTOMERtableasanexample:
select COUNT(*) as NumbersofCustomers from CUSTOMER
11.1.6 TheGROUPBYStatement
AggregatefunctionsoftenneedanaddedGROUPBYstatement.
TheGROUPBYstatementisusedinconjunctionwiththeaggregatefunctionstogrouptheresult-setbyoneormorecolumns.
Syntax
SELECT column_name, aggregate_function(column_name) FROM table_name WHERE column_name operator value GROUP BY column_name
Example:
WeusetheCUSTOMERtableasanexample:
Ifwetrythefollowing:
select FirstName, MAX(AreaCode) from CUSTOMER
Wegetthefollowingerrormessage:
Column 'CUSTOMER.FirstName' is invalid in the select list because it is not contained in either an aggregate function or the GROUP BY clause.
ThesolutionistousetheGROUPBY:
select FirstName, MAX(AreaCode) from CUSTOMER group by FirstName
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11.1.7 TheHAVINGClause
TheHAVINGclausewasaddedtoSQLbecausetheWHEREkeywordcouldnotbeusedwithaggregatefunctions.
Syntax:
SELECT column_name, aggregate_function(column_name) FROM table_name WHERE column_name operator value GROUP BY column_name HAVING aggregate_function(column_name) operator value
WeusetheGRADEtableasanexample:
select * from GRADE
FirstweusetheGROUPBYstatement:
select CourseId, AVG(Grade) from GRADE group by CourseId
Whilethefollowingquery:
select CourseId, AVG(Grade) from GRADE group by CourseId having AVG(Grade)>3
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11.2 User-definedFunctionsINSQL,wemayalsocreateourownfunctions,so-calleduser-definedfunctions.
Auser-definedfunctionisaroutinethatacceptsparameters,performsanaction,suchasacomplexcalculation,andreturnstheresultofthatactionasavalue.Thereturnvaluecaneitherbeascalar(single)valueoratable.Usethisstatementtocreateareusableroutinethatcanbeusedinotherqueries.
InSQLdatabases,auser-definedfunctionprovidesamechanismforextendingthefunctionalityofthedatabaseserverbyaddingafunctionthatcanbeevaluatedinSQLstatements.TheSQLstandarddistinguishesbetweenscalarandtablefunctions.Ascalarfunctionreturnsonlyasinglevalue(orNULL),whereasatablefunctionreturnsa(relational)tablecomprisingzeroormorerows,eachrowwithoneormorecolumns.
StoredProceduresvs.Functions:
• Onlyfunctionscanreturnavalue(usingtheRETURNkeyword). • StoredprocedurescanuseRETURNkeywordbutwithoutanyvaluebeingpassed[1] • FunctionscouldbeusedinSELECTstatements,providedtheydon’tdoanydata
manipulationandalsoshouldnothaveanyOUTorINOUTparameters. • Functionsmustreturnavalue,butforstoredproceduresthisisnotcompulsory. • AfunctioncanhaveonlyINparameters,whilestoredproceduresmayhaveOUTorIN
OUTparameters. • Afunctionisasubprogramwrittentoperformcertaincomputationsandreturna
singlevalue. • Astoredprocedureisasubprogramwrittentoperformasetofactions,andcan
returnmultiplevaluesusingtheOUTparameterorreturnnovalueatall.
User-definedfunctionsinSQLaredeclaredusingtheCREATEFUNCTIONstatement.
Whenwehavecreatedthefunction,wecanusethefunctionthesamewayweusebuilt-infunctions.
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12 TriggersAdatabasetriggeriscodethatisautomaticallyexecutedinresponsetocertaineventsonaparticulartableinadatabase.
SyntaxforcreatingaTrigger:
CREATE TRIGGER <TriggerName> on <TableName> FOR INSERT, UPDATE, DELETE AS … Create your Code here GO
TheTriggerwillautomaticallybeexecutedwhendataisinserted,updatedordeletedinthetableasspecifiedintheTriggerheader.
INSERTEDandDELETED:
Insidetriggerswecanusetwospecialtables:theDELETEDtableandtheINSERTEDtables.SQLServerautomaticallycreatesandmanagesthesetables.Youcanusethesetemporary,
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memory-residenttablestotesttheeffectsofcertaindatamodifications.Youcannotmodifythedatainthesetables.
TheDELETEDtablestorescopiesoftheaffectedrowsduringDELETEandUPDATEstatements.DuringtheexecutionofaDELETEorUPDATEstatement,rowsaredeletedfromthetriggertableandtransferredtotheDELETEDtable.
TheINSERTEDtablestorescopiesoftheaffectedrowsduringINSERTandUPDATEstatements.Duringaninsertorupdatetransaction,newrowsareaddedtoboththeINSERTEDtableandthetriggertable.TherowsintheINSERTEDtablearecopiesofthenewrowsinthetriggertable.
Example:
WewillusetheCUSTOMERtableasanexample:
WewillcreateaTRIGGERthatwillcheckifthePhonenumberisvalidwhenweinsertorupdatedataintheCUSTOMERtable.Thevalidationcheckwillbeverysimple,i.e.,wewillcheckifthePhonenumberislessthan8digits(whichisnormallengthinNorway).IfthePhonenumberislessthan8digits,thefollowingmessage“PhoneNumberisnotvalid”bewritteninplaceofthewrongnumberinthePhonecolumn.
TheTRIGGERbecomessomethinglikethis:
IF EXISTS (SELECT name FROM sysobjects WHERE name = 'CheckPhoneNumber' AND type = 'TR') DROP TRIGGER CheckPhoneNumber GO CREATE TRIGGER CheckPhoneNumber ON CUSTOMER FOR UPDATE, INSERT AS DECLARE @CustomerId int, @Phone varchar(50), @Message varchar(50) set nocount on select @CustomerId = CustomerId from INSERTED select @Phone = Phone from INSERTED
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set @Message = 'Phone Number ' + @Phone + ' is not valid' if len(@Phone) < 8 --Check if Phone Number have less than 8 digits update CUSTOMER set Phone = @Message where CustomerId = @CustomerId set nocount off GO
WetesttheTRIGGERwiththefollowingINSERTINTOstatement:
INSERT INTO CUSTOMER (CustomerNumber, LastName, FirstName, AreaCode, Address, Phone) VALUES ('1003', 'Obama', 'Barak', 51, 'Nevada', '4444')
Theresultsbecome:
Asyoucansee,theTRIGGERworksasexpected.
WetrytoupdatethePhonenumbertoavalidnumber:
update CUSTOMER set Phone = '44444444' where CustomerNumber = '1003'
Theresultsbecome:
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13 CommunicationfromotherApplications
ADatabaseisastructuredwaytostorelotsofinformation.Theinformationisstoredindifferenttables.“Everything”todayisstoredindatabases.
Examples:
• Bank/Accountsystems • InformationinWebpagessuchasFacebook,Wikipedia,YouTube• …lotsofotherexamples
Thismeansweneedtobeabletocommunicatewiththedatabasefromotherapplicationsandprogramminglanguagesinordertoinsert,updateorretrievedatafromthedatabase.
13.1 ODBCODBC(OpenDatabaseConnectivity)isastandardizedinterface(API)foraccessingthedatabasefromaclient.Youcanusethisstandardtocommunicatewithdatabasesfromdifferentvendors,suchasOracle,SQLServer,etc.ThedesignersofODBCaimedtomakeitindependentofprogramminglanguages,databasesystems,andoperatingsystems.
WewillusetheODBCDataSourceAdministrator:
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13.2 MicrosoftExcelMicrosoftExcelhastheabilitytoretrievedatafromdifferentdatasources,includingdifferentdatabasesystems.ItisverysimpletoretrievedatafromSQLServerintoExcelsinceExcelandSQLServerhasthesamevendor(Microsoft).
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14 ReferencesMyBlog:https://www.halvorsen.blog
MicrosoftofficialSQLServerWebsite-http://www.microsoft.com/sqlserver
SQLServerBooksOnline-http://msdn.microsoft.com/en-us/library/ms166020.aspx
SQLServerHelp
w3shools.com-http://www.w3schools.com/sql
Wikipedia–MicrosoftSQLServer-http://en.wikipedia.org/wiki/Microsoft_SQL_Server
Wikipedia-SQL-http://en.wikipedia.org/wiki/SQL
Wikipedia–TransactSQL-http://en.wikipedia.org/wiki/T-SQL
StructuredQueryLanguage
Hans-PetterHalvorsen
Copyright©2017
https://www.halvorsen.blog