Phakathi kweSQL: imizekelo, inkcazo

Xa usebenza kunye neDBMS zentsapho, apho idatha igcinwa kwifomu yetafile, abasebenzisi bahlala bejongana nomsebenzi weesampuli zengqiqo ezingenayo (ezingabandakanywa) kwibanga elithile. Ulwimi lwe-SQL lukuvumela ukuba uchaze isethi ukuba ixabiso ayifanelekanga (kufuneka) lingabakho ngeendlela ezahlukileyo - kwiNgxelo, njenge-Statement efanayo, ukudibanisa kweemeko kuncinci, kunye ne-Operator SQL phakathi. Inkcazo nemimiselo kweli nqaku iya kunikwa kwixesha lokugqibela.

I-"Between" i-SQL: i-syntax, imiqobo

Umsebenzisi phakathi kwe-SQL uguqulelwe ngokoqobo "phakathi". Ukusetyenziswa kwayo kukuvumela ukuba usethe "Ukuphuma kunye nokuya" kwintsimi ethile, kwaye ukuba ixabiso elilandelayo liwela kwibanga, isiqendu siya kuba "Yi nyaniso" kwaye ixabiso liya kugqiba ekukhetheni kokugqibela.

I-syntax yomsebenzisi ilula kakhulu:

Njengoko ubona, emva kwegama eliphambili phakathi kwalo kuyimfuneko ukucacisa ixabiso lentambo engaphantsi kwoluhlu, ngoko-NA kunye nenani lomda ophezulu.

Makhe sibhale uluhlu lweedatha umqhubi we-SQL angasebenza kunye:

1. Ngeenombolo - ezipheleleyo kunye neqhekeza.
2. Ngemihla.
3. Ngombhalo.

Umsebenzisi onikeziweyo phakathi kwe-SQL unempawu ezithile. Masiqhelane nabo:

1. Xa usebenza kunye namanani kunye nemini, ixabiso le-"From and to" "lifakwe kwisampuli.
2. Ubungakanani bemida engaphantsi kwoluhlu kufuneka lube ngaphantsi kwexabiso lentambo ephezulu, kungenjalo akukho nto iya kuveliswa, kuba imeko ayiyiyo imigaqo. Ukunyamekela okuthethekileyo kufuneka kuthathelwe xa izixhobo ezifakiwe zifakwe kwiimeko endaweni yexabiso elithile.

Xa usebenza ngetekisi, ixabiso lomda ophezulu woluhlu aluyi kufakwa ekukhetheni, ngaphandle kokuba kuchazwe ngokuchanekileyo ngokuchanekileyo. Kwimacandelo alandelayo, siya kuqwalasela le nkcukacha ngokubanzi.

Ukukhethwa kwamanani kunye nemihla kwibanga elithile

Lungiselela itafile kunye nedatha kubaphathi abasebenza kwintlangano. Itheyibhile iya kuba nesakhiwo esilandelayo:

Gcwalisa etafileni ngedatha elandelayo:

Masenze umbuzo we- sql phakathi, oya kusinceda sikhethe bonke abasebenzi abanabantwana aba-2 okanye abathathu:

Isiphumo siya kuba nemigca emithathu kunye nedatha kubasebenzi abanegama likaShumilin, iTropnikov neAvdeeva.

Ngoku siza kukhetha abasebenzi abamkelekileyo ukususela ngoJanuwari 1, 2005 ukuya kuDisemba 31, 2016. Kufuneka kuqatshelwe ukuba i-DBMS eyahlukileyo ikuvumela ukuba urekhode ngokwemiqathango yomhla. Kwiimeko ezininzi, umhla uhamba ngokunyanisekileyo kwimihla-nyanga-nyanga-nyanga yonyaka (okanye ukulungele ngakumbi) kwaye ibhaliwe kwiingcaphuno enye okanye ezimbini. Kwi- database ye - MS Access, usuku lufakwe kwi "#" uphawu. Siza kuyenza umzekelo nje ngokusekelwe kuwo:

Isiphumo siya kuba ngabasebenzi abahlanu, abaqashiweyo ngexesha elichaziweyo, elibandakanya.

Emva koko, makhe sibone indlela i-SQL isebenza ngayo ngemicu.

Sebenza phakathi kwemigca

Umsebenzi oqhelekileyo omele uphathwe ngawo xa usebenza ngamagama omsebenzi kuyimfuneko yokukhetha kuphela abo amagama abo aqala ngencwadi ethile. Siza kuzama ukuzalisekisa isicelo kunye nokukhetha abasebenzi abamaqalo abo aqala ngefayili ukusuka kwi-A ukuya kwi-B:

Isiphumo sisilandelayo:

Njengoko ubona, abasebenzi ababini abanesibini kunye neleta B abafakiwe kwiluhlu. Sisiphi isizathu salokhu? Ingongoma yindlela u-opharetha ngokuthelekisa ngayo imigca yokungalingani. Umgca "B" umfutshane kunomgca "Vinohrad" kwaye ugqityiwe ngeendawo. Kodwa xa uhlela ulandelelwano lwe-alfabhethi, izikhala ziya kuba zikhokela iimpawu, kwaye igama aliyi kufakwa kwisampuli. I-DBMS eyahlukileyo inikezela izisombululo ezahlukeneyo kule ngxaki, kodwa ngokuqhelekileyo ilula kakhulu ukubonisa le ncwadi elandelayo ye-alfabhethi kwimiba:

Xa umbuzo uphendulwa, umphumo uya kusinelisa ngokupheleleyo.

Le ngxaki ikhona kuphela xa isebenzisana nedatha yenkcukacha, kodwa ibonisa ukuba xa usebenza kunye nabaqhubi abasebenzayo abanjengaphakathi, kufuneka uqaphele.