Structured Query Language

Transcription

UniversityCollegeofSoutheastNorway
StructuredQueryLanguage
Hans-PetterHalvorsen,2016.01.08
TheTutorialisavailableOnline:http://home.hit.no/~hansha/?tutorial=sql
http://home.hit.no/~hansha
TableofContents
1
2
IntroductiontoSQL...........................................................................................................5
1.1
DataDefinitionLanguage(DDL)..................................................................................7
1.2
DataManipulationLanguage(DML)...........................................................................7
IntroductiontoSQLServer................................................................................................8
2.1
3
SQLServerManagementStudio.................................................................................9
2.1.1
CreateanewDatabase......................................................................................10
2.1.2
Queries..............................................................................................................11
CREATETABLE.................................................................................................................12
3.1
DatabaseModelling..................................................................................................14
3.2
CreateTablesusingtheDesignerTools....................................................................16
3.3
SQLConstraints.........................................................................................................16
3.3.1
PRIMARYKEY.....................................................................................................17
3.3.2
FOREIGNKEY.....................................................................................................18
3.3.3
NOTNULL/RequiredColumns.........................................................................21
3.3.4
UNIQUE.............................................................................................................22
3.3.5
CHECK................................................................................................................24
3.3.6
DEFAULT............................................................................................................26
3.3.7
AUTOINCREMENTorIDENTITY.........................................................................27
3.4
ALTERTABLE.............................................................................................................28
4
INSERTINTO....................................................................................................................30
5
UPDATE...........................................................................................................................32
2
3
TableofContents 6
DELETE.............................................................................................................................34
7
SELECT.............................................................................................................................36
7.1
TheORDERBYKeyword............................................................................................38
7.2
SELECTDISTINCT.......................................................................................................39
7.3
TheWHEREClause....................................................................................................39
7.3.1
Operators..........................................................................................................40
7.3.2
LIKEOperator....................................................................................................40
7.3.3
INOperator........................................................................................................41
7.3.4
BETWEENOperator...........................................................................................41
7.4
Wildcards..................................................................................................................41
7.5
AND&OROperators................................................................................................42
7.6
SELECTTOPClause....................................................................................................43
7.7
Alias..........................................................................................................................44
7.8
Joins..........................................................................................................................44
7.8.1
8
DifferentSQLJOINs...........................................................................................45
SQLScripts.......................................................................................................................47
8.1
UsingComments.......................................................................................................47
8.1.1
Single-linecomment..........................................................................................47
8.1.2
Multiple-linecomment......................................................................................47
8.2
Variables...................................................................................................................48
8.3
Built-inGlobalVariables...........................................................................................49
8.3.1
8.4
@@IDENTITY.....................................................................................................49
FlowControl.............................................................................................................50
8.4.1
IF–ELSE.............................................................................................................50
8.4.2
WHILE................................................................................................................51
8.4.3
CASE...................................................................................................................52
Tutorial:StructuredQueryLanguage(SQL)
4
8.4.4
9
TableofContents CURSOR.............................................................................................................53
Views...............................................................................................................................55
9.1
10
UsingtheGraphicalDesigner...................................................................................56
StoredProcedures........................................................................................................60
10.1
11
NOCOUNTON/NOCOUNTOFF..............................................................................63
Functions......................................................................................................................65
11.1
Built-inFunctions..................................................................................................65
11.1.1
StringFunctions.............................................................................................65
11.1.2
DateandTimeFunctions...............................................................................66
11.1.3
MathematicsandStatisticsFunctions...........................................................66
11.1.4
AVG()..............................................................................................................67
11.1.5
COUNT().........................................................................................................67
11.1.6
TheGROUPBYStatement..............................................................................68
11.1.7
TheHAVINGClause........................................................................................69
11.2
User-definedFunctions.........................................................................................70
12
Triggers.........................................................................................................................71
13
CommunicationfromotherApplications.....................................................................74
13.1
ODBC.....................................................................................................................74
13.2
MicrosoftExcel......................................................................................................75
14
References....................................................................................................................77
1 IntroductiontoSQL
SQL(StructuredQueryLanguage)isadatabasecomputerlanguagedesignedformanaging
datainrelationaldatabasemanagementsystems(RDBMS).
SQL,isastandardizedcomputerlanguagethatwasoriginallydevelopedbyIBMforquerying,
alteringanddefiningrelationaldatabases,usingdeclarativestatements.
SQLispronounced/ˌɛskjuːˈɛl/ (letterbyletter) or/ˈsiːkwəl/ (asaword).
WhatcanSQLdo?
•
•
•
•
•
SQLcanexecutequeriesagainstadatabase
SQLcanretrievedatafromadatabase
SQLcaninsertrecordsinadatabase
SQLcanupdaterecordsinadatabase
SQLcandeleterecordsfromadatabase
5
6
•
•
•
•
•
IntroductiontoSQL SQLcancreatenewdatabases
SQLcancreatenewtablesinadatabase
SQLcancreatestoredproceduresinadatabase
SQLcancreateviewsinadatabase
SQLcansetpermissionsontables,procedures,andviews
EvenifSQLisastandard,manyofthedatabasesystemsthatexisttodayimplementtheir
ownversionoftheSQLlanguage.InthisdocumentwewillusetheMicrosoftSQLServeras
anexample. Therearelotsofdifferentdatabasesystems,orDBMS–DatabaseManagementSystems,
suchas:
•
•
•
•
•
•
•
MicrosoftSQLServer
o Enterprise,Developerversions,etc.
o Expressversionisfreeofcharge
Oracle
MySQL(Oracle,previouslySunMicrosystems)-MySQLcanbeusedfreeofcharge
(opensourcelicense),WebsitesthatuseMySQL:YouTube,Wikipedia,Facebook
MicrosoftAccess
IBMDB2
Sybase
…lotsofothersystems
InthisTutorialwewillfocusonMicrosoftSQLServer.SQLServerusesT-SQL(Transact-SQL).
T-SQLisMicrosoft'sproprietaryextensiontoSQL.T-SQLisverysimilartostandardSQL,but
inadditionitsupportssomeextrafunctionality,built-infunctions,etc.
7
IntroductiontoSQL OtherusefulTutorialsaboutdatabases:
•
•
IntroductiontoDatabaseSystems
DatabaseCommunicationinLabVIEW
TheseTutorialsarelocatedat:http://home.hit.no/~hansha 1.1 DataDefinitionLanguage(DDL)
TheDataDefinitionLanguage(DDL)managestableandindexstructure.Themostbasic
itemsofDDLaretheCREATE,ALTER,RENAMEandDROPstatements:
•
•
•
CREATEcreatesanobject(atable,forexample)inthedatabase. DROPdeletesanobjectinthedatabase,usuallyirretrievably. ALTERmodifiesthestructureanexistingobjectinvariousways—forexample,adding
acolumntoanexistingtable. 1.2 DataManipulationLanguage(DML)
TheDataManipulationLanguage(DML)isthesubsetofSQLusedtoadd,updateanddelete
data.
TheacronymCRUDreferstoallofthemajorfunctionsthatneedtobeimplementedina
relationaldatabaseapplicationtoconsideritcomplete.Eachletterintheacronymcanbe
mappedtoastandardSQLstatement:
Operation
Create
SQL
INSERTINTO
Read(Retrieve)
Update
Delete(Destroy)
SELECT UPDATE DELETE
Description
insertsnewdataintoa
database
extractsdatafromadatabase
updatesdatainadatabase
deletesdatafromadatabase
2 IntroductiontoSQLServer
MicrosoftisthevendorofSQLServer. WehavedifferenteditionsofSQLServer,whereSQLServerExpressisfreetodownloadand
use.
SQLServerusesT-SQL(Transact-SQL).T-SQLisMicrosoft'sproprietaryextensiontoSQL.TSQLisverysimilartostandardSQL,butinadditionitsupportssomeextrafunctionality,builtinfunctions,etc.T-SQLexpandsontheSQLstandardtoincludeproceduralprogramming,
localvariables,varioussupportfunctionsforstringprocessing,dateprocessing,
mathematics,etc.
SQLServerconsistsofaDatabaseEngineandaManagementStudio(andlotsofotherstuff
whichwewillnotmentionhere).TheDatabaseenginehasnographicalinterface-itisjusta
servicerunninginthebackgroundofyourcomputer(preferableontheserver).The
ManagementStudioisgraphicaltoolforconfiguringandviewingtheinformationinthe
database.Itcanbeinstalledontheserverorontheclient(orboth).
8
9
IntroductiontoSQLServer 2.1 SQLServerManagementStudio
SQLServerManagementStudioisaGUItoolincludedwithSQLServerforconfiguring,
managing,andadministeringallcomponentswithinMicrosoftSQLServer.Thetoolincludes
bothscripteditorsandgraphicaltoolsthatworkwithobjectsandfeaturesoftheserver.As
mentionedearlier,versionofSQLServerManagementStudioisalsoavailableforSQLServer
ExpressEdition,forwhichitisknownasSQLServerManagementStudioExpress.
AcentralfeatureofSQLServerManagementStudioistheObjectExplorer,whichallowsthe
usertobrowse,select,andactuponanyoftheobjectswithintheserver.Itcanbeusedto
visuallyobserveandanalyzequeryplansandoptimizethedatabaseperformance,among
others.SQLServerManagementStudiocanalsobeusedtocreateanewdatabase,alterany
existingdatabaseschemabyaddingormodifyingtablesandindexes,oranalyze
performance.ItincludesthequerywindowswhichprovideaGUIbasedinterfacetowrite
andexecutequeries.
WhencreatingSQLcommandsandqueries,the“QueryEditor”(select“NewQuery”from
theToolbar)isused(showninthefigureabove).
WithSQLandthe“QueryEditor”wecandoalmosteverythingwithcode,butsometimesitis
alsoagoodideatousethedifferentDesignertoolsinSQLtohelpusdotheworkwithout
coding(somuch).
10
2.1.1
IntroductiontoSQLServer CreateanewDatabase
ItisquitesimpletocreateanewdatabaseinMicrosoftSQLServer.Justright-clickonthe
“Databases”nodeandselect“NewDatabase…”
Therearelotsofsettingsyoumaysetregardingyourdatabase,buttheonlyinformationyou
mustfillinisthenameofyourdatabase:
11
IntroductiontoSQLServer YoumayalsousetheSQLlanguagetocreateanewdatabase,butsometimesitiseasierto
justusethebuilt-infeaturesintheManagementStudio.
2.1.2
Queries
InordertomakeanewSQLquery,selectthe“NewQuery”buttonfromtheToolbar.
HerewecanwriteanykindofqueriesthatissupportedbytheSQLlanguage.
3 CREATETABLE
Beforeyoustartimplementingyourtablesinthedatabase,youshouldalwaysspendsome
timedesignyourtablesproperlyusingadesigntoollike,e.g.,ERwin,ToadDataModeler,
PowerDesigner,Visio,etc.ThisiscalledDatabaseModeling.
TheCREATETABLEstatementisusedtocreateatableinadatabase.
Syntax:
CREATE TABLE
(
column_name1
column_name2
column_name3
....
)
table_name
data_type,
data_type,
data_type,
Thedatatypespecifieswhattypeofdatathecolumncanhold.
12
13
CREATETABLE Youhavespecialdatatypesfornumbers,textdates,etc.
Examples:
•
•
•
•
Numbers:int,float
Text/Stings:varchar(X)–whereXisthelengthofthestring
Dates:datetime
etc.
Example:
Wewanttocreateatablecalled“CUSTOMER”whichhasthefollowingcolumnsanddata
types:
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.
14
•
•
•
•
CREATETABLE o “Always”useIntegerandIdentity(1,1)forPrimaryKeys.UseUNIQUE
constraintforothercolumnsthatneedstobeunique,e.g.RoomNumber
SpecifyRequiredColumns(NOTNULL)–i.e.,whichcolumnsthatneedtohavedata
ornot
Standardizeonfew/theseDataTypes:int,float,varchar(x),datetime,bit
UseEnglishfortableandcolumnnames
Avoidabbreviations!(UseRoomNumber–notRoomNo,RoomNr,...)
3.1 DatabaseModelling
Asmentioninthebeginningofthechapter,youshouldalwaysstartwithdatabasemodelling
beforeyoustartimplementingthetablesinadatabasesystem.
BelowweseeadatabasemodelincreatedwithERwin.
Withthistoolwecantransferthedatabasemodelastablesintodifferentdatabasesystems,
suchase.g.,SQLServer.CAERwinDataModelerCommunityEditionisfreewitha25objects
limit.IthassupportforOracle,SQLServer,MySQL,ODBCandSybase.
15
CREATETABLE BelowweseethesametablesinsidethedesigntoolinSQLServer.
16
CREATETABLE 3.2 CreateTablesusingtheDesignerTools
Evenifyoucando“everything”usingtheSQLlanguage,itissometimeseasiertodoitinthe
designertoolsintheManagementStudioinSQLServer.
Insteadofcreatingascriptyoumayaswelleasilyusethedesignerforcreatingtables.
Step1:Select“NewTable…”:
Step2:Next,thetabledesignerpopsupwhereyoucanaddcolumns,datatypes,etc.
InthisdesignerwemayalsospecifyColumnNames,DataTypes,etc.
Step3:SavethetablebyclickingtheSavebutton.
3.3 SQLConstraints
Constraintsareusedtolimitthetypeofdatathatcangointoatable.
17
CREATETABLE Constraintscanbespecifiedwhenatableiscreated(withtheCREATETABLEstatement)or
afterthetableiscreated(withtheALTERTABLEstatement).
Herearethemostimportantconstraints:
•
•
•
•
•
•
•
PRIMARYKEY
NOTNULL
UNIQUE
FOREIGNKEY
CHECK
DEFAULT
IDENTITY
Inthesectionsbelowwewillexplainsomeoftheseindetail.
3.3.1
PRIMARYKEY
ThePRIMARYKEYconstraintuniquelyidentifieseachrecordinadatabasetable.
Primarykeysmustcontainuniquevalues.Itisnormaltojustuserunningnumbers,like1,2,
3,4,5,…asvaluesinPrimaryKeycolumn.Itisagoodideatoletthesystemhandlethisfor
youbyspecifyingthatthePrimaryKeyshouldbesettoidentity(1,1).IDENTITY(1,1)means
thefirstvaluewillbe1andthenitwillincrementby1.
Eachtableshouldhaveaprimarykey,andeachtablecanhaveonlyONEprimarykey.
IfwetakeacloserlookattheCUSTOMERtablecreatedearlier:
CREATE TABLE [CUSTOMER]
(
AreaCode int NULL,
)
GO
Asyouseeweusethe“PrimaryKey”keywordtospecifythatacolumnshouldbethe
PrimaryKey.
18
CREATETABLE SettingPrimaryKeysintheDesignerTools:
IfyouusetheDesignertoolsinSQLServer,youcaneasilysettheprimaryKeyinatablejust
byright-clickandselect“SetprimaryKey”. TheprimaryKeycolumnwillthenhaveasmallkey infronttoillustratethatthiscolumnis
aPrimaryKey.
3.3.2
FOREIGNKEY
AFOREIGNKEYinonetablepointstoaPRIMARYKEYinanothertable.
Example:
WewillcreateaCREATETABLEscriptforthesetables:
19
CREATETABLE SCHOOL:
CREATE TABLE SCHOOL
(
SchoolId int IDENTITY(1,1) PRIMARY KEY,
SchoolName varchar(50) NOT NULL UNIQUE,
Description varchar(1000) 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
TheFOREIGNKEYconstraintisusedtopreventactionsthatwoulddestroylinksbetween
tables.
TheFOREIGNKEYconstraintalsopreventsthatinvaliddatafrombeinginsertedintothe
foreignkeycolumn,becauseithastobeoneofthevaluescontainedinthetableitpointsto.
SettingForeignKeysintheDesignerTools:
Ifyouwanttousethedesigner,right-clickonthecolumnthatyouwanttobetheForeign
Keyandselect“Relationships…”: Tutorial:StructuredQueryLanguage(SQL)
20
CREATETABLE Thefollowingwindowpopsup(ForeignKeyRelationships):
Clickonthe“Add”buttonandthenclickonthesmall“…”button.Thenthefollowingwindow
popsup(TablesandColumns):
21
CREATETABLE HereyouspecifytheprimaryKeyColumninthePrimaryKeytableandtheForeignKey
ColumnintheForeignKeytable.
3.3.3
NOTNULL/RequiredColumns
TheNOTNULLconstraintenforcesacolumntoNOTacceptNULLvalues.
TheNOTNULLconstraintenforcesafieldtoalwayscontainavalue.Thismeansthatyou
cannotinsertanewrecord,orupdatearecordwithoutaddingavaluetothisfield.
(
AreaCode int NULL,
)
GO
22
CREATETABLE Weseethat“CustomerNumber”,“LastName”and“FirstName”issetto“NOTNULL”,this
meansthesecolumnsneedstocontaindata.While“AreaCode”,“Address”and“Phone”may
beleftempty,i.e,theydon’tneedtofilledout.
Note!AprimarykeycolumncannotcontainNULLvalues.
SettingNULL/NOTNULLintheDesignerTools:
IntheTableDesigneryoucaneasilysetwhichcolumnsthatshouldallowNULLornot:
3.3.4
UNIQUE
TheUNIQUEconstraintuniquelyidentifieseachrecordinadatabasetable.TheUNIQUEand
PRIMARYKEYconstraintsbothprovideaguaranteeforuniquenessforacolumnorsetof
columns.
APRIMARYKEYconstraintautomaticallyhasaUNIQUEconstraintdefinedonit.
Note!YoucanhavemanyUNIQUEconstraintspertable,butonlyonePRIMARYKEY
constraintpertable.
(
AreaCode int NULL,
23
CREATETABLE Phone varchar(50) NULL,
)
GO
Weseethatthe“CustomerNumber”issettoUNIQUE,meaningeachcustomermusthavea
uniqueCustomerNumber.Example:
SettingUNIQUEintheDesignerTools:
Ifyouwanttousethedesigner,right-clickonthecolumnthatyouwanttobeUNIQUEand
select“Indexes/Keys…”: Thenclick“Add”andthensetthe“IsUnique”propertyto“Yes”:
24
CREATETABLE 3.3.5
CHECK
TheCHECKconstraintisusedtolimitthevaluerangethatcanbeplacedinacolumn.
IfyoudefineaCHECKconstraintonasinglecolumnitallowsonlycertainvaluesforthis
column.
IfyoudefineaCHECKconstraintonatableitcanlimitthevaluesincertaincolumnsbased
onvaluesinothercolumnsintherow.
Example:
(
CustomerNumber int NOT NULL UNIQUE CHECK(CustomerNumber>0),
AreaCode int NULL,
)
GO
Inthiscase,whenwetrytoinsertaCustomerNumberlessthanzerowewillgetanerror
message.
SettingCHECKconstraintsintheDesignerTools:
Ifyouwanttousethedesigner,right-clickonthecolumnwhereyouwanttosetthe
constraintsandselect“CheckConstraints…”:
25
CREATETABLE Thenclick“Add”andthenclick“…”inordertoopentheExpressionwindow:
IntheExpressionwindowyoucantypeintheexpressionyouwanttouse:
26
CREATETABLE 3.3.6
DEFAULT
TheDEFAULTconstraintisusedtoinsertadefaultvalueintoacolumn.
Thedefaultvaluewillbeaddedtoallnewrecords,ifnoothervalueisspecified.
Example:
(
Country varchar(20) DEFAULT 'Norway',
AreaCode int NULL,
)
GO
SettingDEFAULTvaluesintheDesignerTools:
Selectthecolumnandgointothe“ColumnProperties”:
27
3.3.7
CREATETABLE AUTOINCREMENTorIDENTITY
Veryoftenwewouldlikethevalueoftheprimarykeyfieldtobecreatedautomaticallyevery
timeanewrecordisinserted.
Example:
(
AreaCode int NULL,
)
GO
Asshownbelow,weusetheIDENTITY()forthis.IDENTITY(1,1)meansthefirstvaluewillbe1
andthenitwillincrementby1.
Settingidentity(1,1)intheDesignerTools:
WecanusethedesignertoolstospecifythataPrimaryKeyshouldbeanidentitycolumn
thatisautomaticallygeneratedbythesystemwhenweinsertdataintothetable.
ClickonthecolumninthedesignerandgointotheColumnPropertieswindow:
28
CREATETABLE 3.4 ALTERTABLE
TheALTERTABLEstatementisusedtoadd,delete,ormodifycolumnsinanexistingtable.
Toaddacolumninatable,usethefollowingsyntax:
ALTER TABLE table_name
ADD column_name datatype
Todeleteacolumninatable,usethefollowingsyntax(noticethatsomedatabasesystems
don'tallowdeletingacolumn):
DROP COLUMN column_name
Tochangethedatatypeofacolumninatable,usethefollowingsyntax:
ALTER COLUMN column_name datatype
IfweuseCREATETABLEandthetablealreadyexistsinthetablewewillgetanerror
message,soifwecombineCREATETABLEandALTERTABLEwecancreaterobustdatabase
scriptsthatgivesnoerrors,astheexampleshownbelow:
if not exists (select * from dbo.sysobjects where id = object_id(N'[CUSTOMER]') and
OBJECTPROPERTY(id, N'IsUserTable') = 1)
(
CustomerId int PRIMARY KEY,
AreaCode int 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
29
Else
ALTER TABLE CUSTOMER ADD CustomerNumber int
GO
...
CREATETABLE 4 INSERTINTO
TheINSERTINTOstatementisusedtoinsertanewrowinatable.
ItispossibletowritetheINSERTINTOstatementintwoforms. Thefirstformdoesn'tspecifythecolumnnameswherethedatawillbeinserted,onlytheir
values:
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:
30
31
INSERTINTO i.e.,weneedtoincludeatleast“CustomerNumber”,“LastName”and“FirstName”.
“CustomerId”issetto“identity(1,1)”andthereforevaluesforthiscolumnaregeneratedby
thesystem.
InsertDataintheDesignerTools:
Whenyouhavecreatedthetablesyoucaneasilyinsertdataintothemusingthedesigner
tools.Right-clickonthespecifictableandselect“EditTop200Rows”:
Thenyoucanenterdatainatableformat,similarto,e.g.,MSExcel:
5 UPDATE
TheUPDATEstatementisusedtoupdateexistingrecordsinatable.
Thesyntaxisasfollows:
UPDATE table_name
SET column1=value, column2=value2,...
WHERE some_column=some_value
Note!NoticetheWHEREclauseintheUPDATEsyntax.TheWHEREclausespecifieswhich
recordorrecordsthatshouldbeupdated.IfyouomittheWHEREclause,allrecordswillbe
updated!
Example:
update CUSTOMER set AreaCode=46 where CustomerId=2
Beforeupdate:
Afterupdate:
Ifyoudon’tincludetheWHEREclausetheresultbecomes:
→SomakesuretoincludetheWHEREclausewhenusingtheUPDATEcommand!
32
33
UPDATE UpdateDataintheDesignerTools:
Thesamewayyouinsertdatayoucanalsoupdatethedata.Right-clickonthespecifictable
andselect“EditTop200Rows”:
Thenyoucanchangeyourdata:
6 DELETE
TheDELETEstatementisusedtodeleterowsinatable.
Syntax:
DELETE FROM table_name
WHERE some_column=some_value
Note!NoticetheWHEREclauseintheDELETEsyntax.TheWHEREclausespecifieswhich
recordorrecordsthatshouldbedeleted.IfyouomittheWHEREclause,allrecordswillbe
deleted!
Example:
delete from CUSTOMER where CustomerId=2
Beforedelete:
Afterdelete:
DeleteAllRows:
Itispossibletodeleteallrowsinatablewithoutdeletingthetable.Thismeansthatthe
tablestructure,attributes,andindexeswillbeintact:
DELETE FROM table_name
Note!Makesuretodothisonlywhenyoureallymeanit!YoucannotUNDOthisstatement!
DeleteDataintheDesignerTools:
Youdeletedatainthedesignerbyright-clickontherowandselect“Delete”:
34
35
DELETE Tutorial:StructuredQueryLanguage(SQL)
7 SELECT
TheSELECTstatementisprobablythemostusedSQLcommand.TheSELECTstatementis
usedforretrievingrowsfromthedatabaseandenablestheselectionofoneormanyrowsor
columnsfromoneormanytablesinthedatabase.
WewillusetheCUSTOMERtableasanexample. TheCUSTOMERtablehasthefollowingcolumns:
TheCUSTOMERtablecontainsthefollowingdata:
Example:
select * from CUSTOMER
ThissimpleexamplegetsallthedatainthetableCUSTOMER.Thesymbol“*”isusedwhen
youwanttogetallthecolumnsinthetable.
36
37
SELECT Ifyouonlywantafewcolumns,youmayspecifythenamesofthecolumnsyouwantto
retrieve,example:
select CustomerId, LastName, FirstName from CUSTOMER
SointhesimplestformwecanusetheSELECTstatementasfollows:
select <column_names> from <table_names>
Ifwewantallcolumns,weusethesymbol“*”
Note!SQLisnotcasesensitive.SELECTisthesameasselect.
ThefullsyntaxoftheSELECTstatementiscomplex,butthemainclausescanbesummarized
as:
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:
38
SELECT ASelectqueryisautomaticallycreatedforyouwhichyoucaneditifyouwantto.
7.1 TheORDERBYKeyword
Ifyouwantthedatatoappearinaspecificorderyouneedtousethe“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”).Ifyouwantthe
ordertobeopposite,i.e.,descending,thenyouneedtousethe“desc”keyword.
39
SELECT select * from CUSTOMER order by LastName desc
7.2 SELECTDISTINCT
Inatable,someofthecolumnsmaycontainduplicatevalues.Thisisnotaproblem,
however,sometimesyouwillwanttolistonlythedifferent(distinct)valuesinatable.
TheDISTINCTkeywordcanbeusedtoreturnonlydistinct(different)values.
select distinct <column_names> from <table_names>
Example:
select distinct FirstName from CUSTOMER
7.3 TheWHEREClause
TheWHEREclauseisusedtoextractonlythoserecordsthatfulfillaspecifiedcriterion.
select <column_names>
from <table_name>
where <column_name> operator value
Example:
select * from CUSTOMER where CustomerNumber='1001'
40
SELECT Note!SQLusessinglequotesaroundtextvalues,asshownintheexampleabove.
7.3.1
Operators
WiththeWHEREclause,thefollowingoperatorscanbeused:
Operator
=
<>
>
<
>=
<=
BETWEEN
LIKE
IN
Description
Equal
Notequal Greaterthan Lessthan Greaterthanorequal Lessthanorequal Betweenaninclusiverange Searchforapattern 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)both
beforeandafterthepattern.
41
SELECT select * from CUSTOMER where LastName like '%a%'
YoumayalsocombinewiththeNOTkeyword,example:
select * from CUSTOMER where LastName not like '%a%'
7.3.3
INOperator
TheINoperatorallowsyoutospecifymultiplevaluesinaWHEREclause.
Syntax:
FROM table_name
WHERE column_name IN (value1,value2,...)
7.3.4
BETWEENOperator
TheBETWEENoperatorselectsarangeofdatabetweentwovalues.Thevaluescanbe
numbers,text,ordates.
Syntax:
FROM table_name
WHERE column_name
BETWEEN value1 AND value2
7.4 Wildcards
SQLwildcardscansubstituteforoneormorecharacterswhensearchingfordataina
database.
Note!SQLwildcardsmustbeusedwiththeSQLLIKEoperator.
WithSQL,thefollowingwildcardscanbeused:
42
Wildcard
%
_
[charlist]
[^charlist]
or
[!charlist]
SELECT Description
Asubstituteforzeroormorecharacters
Asubstituteforexactlyonecharacter
Anysinglecharacterincharlist
Anysinglecharacternotincharlist
Examples:
SELECT * FROM CUSTOMER WHERE LastName LIKE 'J_cks_n'
SELECT * FROM CUSTOMER WHERE CustomerNumber LIKE '[10]%'
7.5 AND&OROperators
TheANDoperatordisplaysarecordifboththefirstconditionandthesecondconditionis
true.
TheORoperatordisplaysarecordifeitherthefirstconditionorthesecondconditionistrue.
Examples:
select * from CUSTOMER where LastName='Smith' and FirstName='John'
select * from CUSTOMER where LastName='Smith' or FirstName='John'
43
SELECT CombiningAND&OR:
YoucanalsocombineANDandOR(useparenthesistoformcomplexexpressions).
Example:
where LastName='Smith' and (FirstName='John' or FirstName='Smith')
7.6 SELECTTOPClause
TheTOPclauseisusedtospecifythenumberofrecordstoreturn.
TheTOPclausecanbeveryusefulonlargetableswiththousandsofrecords.Returninga
largenumberofrecordscanimpactonperformance.
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
44
SELECT 7.7 Alias
Youcangiveatableoracolumnanothernamebyusinganalias.Thiscanbeagoodthingto
doifyouhaveverylongorcomplextablenamesorcolumnnames.
Analiasnamecouldbeanything,butusuallyitisshort.
SQLAliasSyntaxforTables:
FROM table_name
AS alias_name
SQLAliasSyntaxforColumns:
SELECT column_name AS alias_name
FROM table_name
7.8 Joins
SQLjoinsareusedtoquerydatafromtwoormoretables,basedonarelationshipbetween
certaincolumnsinthesetables.
45
SELECT 7.8.1
DifferentSQLJOINs
Beforewecontinuewithexamples,wewilllistthetypesofJOINyoucanuse,andthe
differencesbetweenthem.
•
•
•
•
JOIN:Returnrowswhenthereisatleastonematchinbothtables
LEFTJOIN:Returnallrowsfromthelefttable,eveniftherearenomatchesinthe
righttable
RIGHTJOIN:Returnallrowsfromtherighttable,eveniftherearenomatchesinthe
lefttable
FULLJOIN:Returnrowswhenthereisamatchinoneofthetables
Example:
Given2tables:
•
•
SCHOOL
CLASS
46
SELECT Thediagramisshownbelow:
Wewanttogetthefollowinginformationusingaquery:
SchoolName
ClassName
…
…
…
…
InordertogetinformationfrommorethanonetableweneedtousetheJOIN.TheJOINis
usedtojointheprimarykeyinonetablewiththeforeignkeyinanothertable.
select
SCHOOL.SchoolName,
CLASS.ClassName
from
SCHOOL
INNER JOIN CLASS ON SCHOOL.SchoolId = CLASS.SchoolId
8 SQLScripts
ASQLscriptisacollectionofSQLstatementsthatyoucanexecuteinoneoperation.Youcan
useanykindofSQLcommands,suchasinsert,select,delete,update,etc.Inadditionyou
candefineandusevariables,andyoumayalsouseprogramflowlikeIf-Else,etc.Youmay
alsoaddcommentstomakethescripteasiertoreadandunderstand.
8.1 UsingComments
UsingcommentsinyouSQLscriptisimportanttomakethescripteasiertoreadand
understand.
InSQLwecanuse2differentkindsofcomments:
•
•
Single-linecomment
Multiple-linecomment
8.1.1
Single-linecomment
Wecancommentonelineatthetimeusing“--”beforethetextyouwanttocommentout.
Syntax:
-- text_of_comment
8.1.2
Multiple-linecomment
Wecancommentseverallineusing“/*”inthestartofthecommentand“*/”intheendof
thecomment.
Syntax:
/*
text_of_comment
text_of_comment
*/
47
48
SQLScripts 8.2 Variables
TheabilitytousingvariablesinSQLisapowerfulfeature.Youneedtousethekeyword
DECLAREwhenyouwanttodefinethevariables.Localvariablesmusthavethethesymbol
“@”asaprefix.Youalsoneedtospecifyadatatypeforyourvariable(int,varchar(x),etc.). Syntaxfordeclaringvariables:
declare @local_variable data_type
Ifyouhavemorethanonevariableyouwanttodeclare:
declare
@myvariable1 data_type,
@myvariable2 data_type,
…
Whenyouwanttoassignvaluestothevariable,youmustuseeitheraSEToraSELECT
statement.
Example:
declare @myvariable int
set @myvariable=4
Ifyouwanttoseethevalueforavariable,youcane.g.,usethePRINTcommandlikethis:
declare @myvariable int
set @myvariable=4
print @myvariable
ThefollowingwillbeshowninSQLServer:
AssigningvariableswithavaluefromaSELECTstatementisveryuseful.
49
SQLScripts 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%'
where LastName LIKE @find
8.3 Built-inGlobalVariables
SQLhavelotsofbuilt-invariablesthatareveryusefultouseinqueriesandscripts.
8.3.1
@@IDENTITY
AfteranINSERT,SELECTINTO,orbulkcopystatementiscompleted,@@IDENTITYcontains
thelastidentityvaluethatisgeneratedbythestatement.Ifthestatementdidnotaffectany
tableswithidentitycolumns,@@IDENTITYreturnsNULL.Ifmultiplerowsareinserted,
generatingmultipleidentityvalues,@@IDENTITYreturnsthelastidentityvaluegenerated.
Example:
Giventotables;SCHOOLandCOURSE:
50
SQLScripts SCHOOLtable:
COURSEtable:
WewanttoinsertanewSchoolintotheSCHOOLtableandwewanttoinsert2newCourses
intheCOURSEtablethatbelongtotheSchoolweinsert.Tofindthe“SchoolId”wecanuse
the@@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, 'MIT101')
insert into COURSE(SchoolId,CourseName) values (@SchoolId, 'MIT201')
Theresultbecomes:
SCHOOLtable:
COURSEtable:
8.4 FlowControl
Aswithotherprogramminglanguagesyoucanusedifferentkindofflowcontrol,suchasIFELSE,WHILE,etc,whichisveryuseful.
8.4.1
IF–ELSE
TheIF-ELSEisveryuseful.Belowweseeanexample:
declare @customerNumber int
51
SQLScripts 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:
IfmorethanonelineofcodeistobeexecutedwithinanIFsentenceyouneedtouse
BEGIN…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
52
SQLScripts end
AsyoucanseethecodeinsidetheWHILEloopisexecutedaslongas“AreaCode”for
CustomerId=1islessthan20.Foreachiterationisthe“AreaCode”forthatcustomer
incrementedwith1.
8.4.3
CASE
TheCASEstatementevaluatesalistofconditionsandreturnsoneofmultiplepossibleresult
expressions.
Example:
Wehavea“GRADE”tablethatcontainsthegradesforeachstudentindifferentcourses:
select GradeId, StudentId, CourseId, Grade from GRADE
Inthe“GRADE”tableisthegradesstoredasnumbers,butsincethestudentsgetgradeswith
thelettersA..F(A=5,B=4,C=3,D=2,E=1,F=0),wewanttoconvertthevaluesinthetable
intolettersusingaCASEstatement:
select
GradeId,
StudentId,
CourseId,
case Grade
when 5 then
when 4 then
when 3 then
when 2 then
when 1 then
when 0 then
else '-'
end
as Grade
from
'A'
'B'
'C'
'D'
'E'
'F'
53
SQLScripts GRADE
8.4.4
CURSOR
Inadvancesscripts,CURSORsmaybeveryuseful.ACURSORworkslikeanadvancedWHILE
loopwhichweusetoiteratethroughtherecordsinoneormoretables.
CURSORSareusedmainlyinstoredprocedures,triggers,andSQLscripts.
Example:
WeusetheCUSTOMERtableasanexample:
WewillcreateaCURSORthatiteratethroughalltherecordsintheCUSTOMERtableand
checkifthePhonenumberconsistsof8digits,ifnotthescriptwillreplacetheinvalidPhone
numberwiththetext“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
54
SQLScripts 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.Declareone
variableforeachresultsetcolumn.
AssociateaSQLcursorwithaSELECTstatementusingtheDECLARECURSOR
statement.TheDECLARECURSORstatementalsodefinesthecharacteristicsofthe
cursor,suchasthecursornameandwhetherthecursorisread-onlyorforward-only.
UsetheOPENstatementtoexecutetheSELECTstatementandpopulatethecursor.
UsetheFETCHINTOstatementtofetchindividualrowsandhavethedataforeach
columnmovedintoaspecifiedvariable.OtherSQLstatementscanthenreference
thosevariablestoaccessthefetcheddatavalues. Whenyouarefinishedwiththecursor,usetheCLOSEstatement.Closingacursor
freessomeresources,suchasthecursor'sresultsetanditslocksonthecurrentrow.
TheDEALLOCATEstatementcompletelyfreesallresourcesallocatedtothecursor,
includingthecursorname.
9 Views
Viewsarevirtualtableforeasieraccesstodatastoredinmultipletables.
SyntaxforcreatingaView:
CREATE VIEW <ViewName>
AS
…
...butitmightbeeasiertodoitinthegraphicalviewdesignerthatarebuiltintoSQL
ManagementStudio.
SyntaxforusingaView:
select * from <MyView> where …
Asshownabove,weuseaVIEWjustlikeweuseanordinarytable.
55
56
Views Example:
WeusetheSCHOOLandCLASStablesasanexampleforourView.WewanttocreateaView
thatlistsalltheexistingschoolsandthebelongingclasses. WecreatetheVIEWusingtheCREATEVIEWcommand:
CREATE VIEW SchoolView
AS
SELECT
SCHOOL.SchoolName,
CLASS.ClassName
FROM
SCHOOL
INNER JOIN CLASS ON SCHOOL.SchoolId = CLASS.SchoolId
Note!Inordertogetinformationfrommorethanonetable,weneedtolinkthetables
togetherusingaJOIN.
9.1 UsingtheGraphicalDesigner
WecreatethesameViewusingthegraphicaldesignerinSQLServerManagementStudio:
57
Views Step1:Right-clickontheViewnodeandselect“NewView…”: Step2:Addnecessarytables:
58
Views Step3:AddColumns,etc.
Step4:SavetheVIEW:
59
Step5:UsetheVIEWinaquery:
select * from SchoolView
Views 10 StoredProcedures
AStoredProcedureisaprecompiledcollectionofSQLstatements.Inastoredprocedureyou
canuseifsentence,declarevariables,etc.
SyntaxforcreatingaStoredProcedure:
CREATE PROCEDURE <ProcedureName>
@<Parameter1> <datatype>
…
declare
@myVariable <datatype>
… Create your Code here
Note!Youneedtousethesymbol“@”beforevariablenames.
SyntaxforusingaStoredProcedure:
EXECUTE <ProcedureName(…)>
Example:
60
61
StoredProcedures WeusetheSCHOOLandCLASStablesasanexampleforourStoredProcedure.Wewantto
createaStoredProcedurethatlistsalltheexistingschoolsandthebelongingclasses. 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)theStoredprocedure
usingtheexecutecommandlikethis:
execute GetAllSchoolClasses
WecanalsocreateaStoreProcedurewithinputparameters.
Example:
62
StoredProcedures Weusethesametablesinthisexample(SCHOOLandCLASS)butnowwewanttolistall
classesforaspecificschool.
TheStoredProcedurebecomes:
CREATE PROCEDURE GetSpecificSchoolClasses
@SchoolName varchar(50)
AS
select
SCHOOL.SchoolName,
CLASS.ClassName
from
SCHOOL
where SchoolName=@SchoolName
order by ClassName
Werun(orexecute)theStoredProcedure:
execute GetSpecificSchoolClasses 'TUC'
or:
execute GetSpecificSchoolClasses 'NTNU'
WhenwetrytocreateaStoredProcedurethatalreadyexistswegetthefollowingerror
message:
There is already an object named 'GetSpecificSchoolClasses' in the database.
Thenwefirstneedtodelete(orDROP)theoldStoredProcedurebeforewecanrecreateit
again.
WecandothismanuallyintheManagementStudioinSQLlikethis:
63
StoredProcedures 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
where SchoolName=@SchoolName
order by ClassName
SoweuseCREATEPROCEDUREtocreateaStoredProcedureandweuseDROPPROCEDURE
todeleteaStoredProcedure.
10.1
NOCOUNTON/NOCOUNTOFF
InadvancedStoredProceduresandScript,performanceisveryimportant.UsingSET
NOCOUNTONandSETNOCOUNTOFFmakestheStoredProcedurerunfaster.
SETNOCOUNTONstopsthemessagethatshowsthecountofthenumberofrowsaffected
byaTransact-SQLstatementorstoredprocedurefrombeingreturnedaspartoftheresult
set.
64
StoredProcedures SETNOCOUNTONpreventsthesendingofDONE_IN_PROCmessagestotheclientforeach
statementinastoredprocedure.Forstoredproceduresthatcontainseveralstatementsthat
donotreturnmuchactualdata,orforproceduresthatcontainTransact-SQLloops,setting
SETNOCOUNTtoONcanprovideasignificantperformanceboost,becausenetworktrafficis
greatlyreduced.
Example:
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’tnormally
needfeedback,spsettingSETNOCOUNTONatthetopinthestoredprocedureisagood
idea.itisalsogoodpracticetoSETNOCOUNTOFFatthebottomofthestoredprocedure.
11 Functions
WithSQLandSQLServeryoucanuselotsofbuilt-infunctionsoryoumaycreateyourown
functions.Herewewilllearntousesomeofthemostusedbuilt-infunctionsandinaddition
wewillcreateourownfunction.
11.1
Built-inFunctions
SQLhasmanybuilt-infunctionsforperformingcalculationsondata.
Wehave2categoriesoffunctions,namelyaggregatefunctionsandscalarfunctions.
Aggregatefunctionsreturnasinglevalue,calculatedfromvaluesinacolumn,whilescalar
functionsreturnasinglevalue,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:
65
66
•
•
•
•
•
•
•
•
•
•
•
•
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
Functions 67
Functions 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(NULLvalueswillnotbe
counted)ofthespecifiedcolumn:
SELECT COUNT(column_name) FROM table_name
TheCOUNT(*)functionreturnsthenumberofrecordsinatable:
SELECT COUNT(*) FROM table_name
68
Functions WeusetheCUSTOMERtableasanexample:
select COUNT(*) as NumbersofCustomers from CUSTOMER
11.1.6 TheGROUPBYStatement
AggregatefunctionsoftenneedanaddedGROUPBYstatement.
TheGROUPBYstatementisusedinconjunctionwiththeaggregatefunctionstogroupthe
result-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
69
Functions 11.1.7 TheHAVINGClause
TheHAVINGclausewasaddedtoSQLbecausetheWHEREkeywordcouldnotbeusedwith
aggregatefunctions.
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
70
11.2
Functions User-definedFunctions
INSQLwemayalsocreateourownfunctions,so-calleduser-definedfunctions.
Auser-definedfunctionisaroutinethatacceptsparameters,performsanaction,suchasa
complexcalculation,andreturnstheresultofthatactionasavalue.Thereturnvaluecan
eitherbeascalar(single)valueoratable.Usethisstatementtocreateareusableroutine
thatcanbeusedinotherqueries.
InSQLdatabases,auser-definedfunctionprovidesamechanismforextendingthe
functionalityofthedatabaseserverbyaddingafunctionthatcanbeevaluatedinSQL
statements.TheSQLstandarddistinguishesbetweenscalarandtablefunctions.Ascalar
functionreturnsonlyasinglevalue(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-in
functions.
12 Triggers
Adatabasetriggeriscodethatisautomaticallyexecutedinresponsetocertaineventsona
particulartableinadatabase.
SyntaxforcreatingaTrigger:
CREATE TRIGGER <TriggerName> on <TableName>
FOR INSERT, UPDATE, DELETE
AS
… Create your Code here
GO
TheTriggerwillautomaticallybeexecutedwhendataisinserted,updatedordeletedinthe
tableasspecifiedintheTriggerheader.
INSERTEDandDELETED:
Insidetriggerswecanusetwospecialtables:theDELETEDtableandtheINSERTEDtables.
SQLServerautomaticallycreatesandmanagesthesetables.Youcanusethesetemporary,
71
72
Triggers memory-residenttablestotesttheeffectsofcertaindatamodifications.Youcannotmodify
thedatainthesetables.
TheDELETEDtablestorescopiesoftheaffectedrowsduringDELETEandUPDATE
statements.DuringtheexecutionofaDELETEorUPDATEstatement,rowsaredeletedfrom
thetriggertableandtransferredtotheDELETEDtable.
TheINSERTEDtablestorescopiesoftheaffectedrowsduringINSERTandUPDATE
statements.Duringaninsertorupdatetransaction,newrowsareaddedtoboththe
INSERTEDtableandthetriggertable.TherowsintheINSERTEDtablearecopiesofthenew
rowsinthetriggertable.
Example:
WewillusetheCUSTOMERtableasanexample:
WewillcreateaTRIGGERthatwillcheckifthePhonenumberisvalidwhenweinsertor
updatedataintheCUSTOMERtable.Thevalidationcheckwillbeverysimple,i.e.,wewill
checkifthePhonenumberislessthan8digits(whichisnormallengthinNorway).Ifthe
Phonenumberislessthan8digits,thefollowingmessage“PhoneNumberisnotvalid”be
writteninplaceofthewrongnumberinthePhonecolumn.
TheTRIGGERbecomessomethinglikethis:
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
73
Triggers 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:
13 Communicationfrom
otherApplications
ADatabaseisastructuredwaytostorelotsofinformation.Theinformationisstoredin
differenttables.“Everything”todayisstoredindatabases.
Examples:
•
•
•
Bank/Accountsystems InformationinWebpagessuchasFacebook,Wikipedia,YouTube
…lotsofotherexamples
Thismeansweneedtobeabletocommunicatewiththedatabasefromotherapplications
andprogramminglanguagesinordertoinsert,updateorretrievedatafromthedatabase. 13.1
ODBC
ODBC(OpenDatabaseConnectivity)isastandardizedinterface(API)foraccessingthe
databasefromaclient.Youcanusethisstandardtocommunicatewithdatabasesfrom
differentvendors,suchasOracle,SQLServer,etc.ThedesignersofODBCaimedtomakeit
independentofprogramminglanguages,databasesystems,andoperatingsystems.
WewillusetheODBCDataSourceAdministrator:
74
75
CommunicationfromotherApplications 13.2
MicrosoftExcel
MicrosoftExcelhastheabilitytoretrievedatafromdifferentdatasources,including
differentdatabasesystems.ItisverysimpletoretrievedatafromSQLServerintoExcelsince
ExcelandSQLServerhasthesamevendor(Microsoft).
76
CommunicationfromotherApplications Tutorial:StructuredQueryLanguage(SQL)
14 References
MyBloghttp://home.hit.no/~hansha 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 77
Hans-PetterHalvorsen,M.Sc.
E-mail:[email protected]
Blog:http://home.hit.no/~hansha UniversityCollegeofSoutheastNorway
www.usn.no

Structured Query Language

Transcription

Similar documents

Quick Intro to SSRS for New WINGAP SQL users

Contact no.(M):9780893349 jalandhar city

Five Techniques for Loading Flat File Data into Oracle Tables

PDF Presentation Slides

2016 SQL stakeholder meeting - summary

The maximum number of users permitted by your

A Scalable and Resilient Platform for Microsoft SQL

document - MWC brokerage event

Design and Generate SQL Server Database