Phakathi SQL: Izibonelo Incazelo

Lapho ukusebenza database zingubudlelwane lapho idatha lilondolozwe amatafula, abasebenzisi babhekana umsebenzi amagugu amasampuli kuhlanganisiwe (kuhlanganisiwe hhayi) yebanga ezithile. SQL ulimi ikuvumela ukuba ukuchaza multiple, okumele (akufanele) basonta ukubaluleka izinto ezahlukene ongazikhetha - opharetha Ngo, Njenge-opharetha, inhlanganisela izimo ezingaphezu - kancane, kanye SQL ngoba Phakathi no-opharetha. Incazelo nezibonelo kulesi sihloko sizogxila enguqulweni yakamuva.

"Phakathi kuka-" opharetha SQL: imikhawulo syntax

Ngokwezwi nezwi igama elithi opharetha phakathi SQL futhi elihunyushwe - "phakathi". Ukusetshenziswa Its kwenza kube nokwenzeka ukuba ubeke umkhawulo "futhi kusukela" emkhakheni othize, futhi uma inani olandelayo uwela ngaphakathi kobubanzi, isilandiso ke azosethwa "boqobo", futhi ukubaluleka bayowa isampula sokugcina.

I-syntax opharetha ezinzima elula:

Njengoba ubona, ngemva elisemqoka phakathi kwakho kumele icacise ukubaluleka umkhawulo engezansi, bese KANYE, futhi mkhawulo.

Bala, iziphi iziphi izinhlobo zedatha opharetha ingasebenza phakathi SQL:

1. Nge izinombolo - inamba futhi ayingxenye.
2. Nge nezinsuku.
3. Ngombhalo.

Yenza lokhu phakathi SQL sitatimende has izici ezithile. Simazi kubo:

1. Lapho ukusebenza ngezinombolo kanye nezinsuku umkhawulo amagugu "futhi kusukela" afakiwe isampuli.
2. Lower ububanzi value kumelwe ibe ngaphansi mkhawulo, kungenjalo lutho kuzovezwa, ngoba isimo akusona eyiqiniso. Kudingeka ukunakekela okukhethekile idinga ukuba, lapho, esikhundleni amagugu specific eziguquguqukayo isimo afakiwe.

Lapho besebenza anenani umbhalo senhlobo engenhla akufakwanga isampuli, uma akachaziwe ngokunembile kakhulu. Sibheka lesi sici izigaba ezilandelayo ngokuningiliziwe.

izinombolo Sample kanye nezinsuku ebangeni elithile

Ulungisa itafula nabaphathi idatha, ukusebenza enhlanganweni. Ithebula kuyodingeka isakhiwo ezilandelayo:

Gcwalisa ithebula nge idatha elandelayo:

Akha umbuzo SQL phakathi, okuyinto kuyosisiza ukuba ukhethe zonke izisebenzi abanezingane 2 noma 3:

Umphumela walokhu uyoba imigqa ezintathu ngedatha ku abasebenzi nezibongo Shumilin, Tropnikov futhi Avdeeva.

Manje khetha abasebenzi etholakele 1 Januwari 2005 kuya ku 31 December 2016. Kufanele kuqashelwe ukuthi yolwazi ehlukene ngezindlela ezahlukene akuvumela ukurekhoda ngokuya izinsuku. Ezimweni eziningi, usuku webutho efomini usuku lwenyanga--ngonyaka (noma kuwusizo kakhudlwana) futhi ezilotshwe izingcaphuno olulodwa noma kabili. I DBMS MS Access usuku zimumethe uphawu "#". Qalisa le isibonelo nje kwezindlu kusekelwe kuyo:

Umphumela walokhu uyoba abasebenzi abahlanu waqoqa ngesikhathi kukonke.

Ngokulandelayo, ake ubone ukuthi isebenza kanjani phakathi SQL izintambo.

Sebenza phakathi amayunithi wezinhlamvu

Inkinga esivame kakhulu okumele ixazululwe uma ukusebenza amagama abasebenzi - isidingo ukhethe labo abamagama ziqale ngohlamvu oluthile kuphela. Futhi sizama akhiphe nombuzo bese ukhetha abasebenzi abamagama siqale isibongo kusuka A kuya B:

Umphumela simiswe ngalendlela lelandzelako:

Njengoba ubona, izisebenzi ezimbili negama B incwadi ohlwini akuzange kufakwe. Siyini isizathu? Iqiniso liwukuthi ngqo ukuthi opharetha eqhathanisa izintambo engalingani. Line "B" string emifushane "Vinogradov" futhi padded. Kodwa lapho ukuhlunga ngama-alfabethi izikhala kuyoba izinhlamvu ngokushesha, futhi igama isampula ngeke kuwele. yolwazi ehlukene ukuhlinzeka ngezindlela ezahlukene ukuxazulula le nkinga, kodwa ngokuvamile kuba yindlela elula ukhombise ukuthembeka incwadi esilandelayo izinhlamvu uhla:

Lapho abulawe, umphumela nombuzo Uyokwanelisa nathi ngokuphelele.

Lokhu ehilelekile ukhona kuphela uma ekusebenteni ngedatha uhlamvu, kodwa kubonisa ukuthi ngisho nalapho ukusebenza ezifana opharetha elula njengoba phakathi, kufanele uqaphele.