Ulimi Lokusebenza Oluhlelekile luyisisekelo se-Behind All Modern Relational Database
Ulimi Lokusebenza Oluhlelekile (SQL) lulimi lwama-yolwazi. Zonke izinqolobane zokuxhumana zanamuhla, ezifaka ukufinyelela, i-FileMaker Pro, iMicrosoft SQL Server kanye ne-Oracle isebenzisa i-SQL njengesisekelo sabo sokwakha esisisekelo. Eqinisweni, ngokuvamile kuyindlela kuphela ongaxhumana ngayo nedatha ngokwayo. Wonke ama-interfaces womsebenzisi odwebayo ohlinzeka ngemininingwane yedatha nokusebenza kokuphathwa kabi akulutho ngaphandle kwabahumushi be-SQL. Bathatha izenzo ozibonisa ngokucacile futhi uguqula imiyalo ye-SQL eqondwe yi-database.
I-SQL ifana ne-English
Kuleli qophelo, ungase ucabange ukuthi awusona isimiso sokufunda futhi ufunda ulimi lohlelo ngokuqinisekile ngeke luphakanyiswe. Ngenhlanhla, engqondweni yayo, i-SQL iyilimi olulula. Inombhalo onqunyelwe wemilayezo, futhi leyo miyalo ifundwa kakhulu futhi ihlelwe ngokufana nemisho yesiNgisi.
Ukwethulwa Kwemininingwane
Ukuqonda i-SQL, kubalulekile ukuthi ube nokuqonda okuyisisekelo ukuthi imininingwane yolwazi isebenza kanjani. Uma ukhululekile ngemigomo efana ne "itafula," "ubudlelwane," kanye "nombuzo," zizwe ukhululekile ukulima phambili! Uma kungenjalo, ungafisa ukufunda i- Database Fundamentals ngaphambi kokuthi uqhubeke.
Ake sibone isibonelo. Ake sithi unedatha elula edizayinelwe ukugcina yokusungula isitolo esilula. Elinye lamatafula ku-database yakho lingase libe nezintengo zezinto kumashalofu akho ezikhokhelwe izinombolo zesitokisi eziyingqayizivele ezikhomba into ngayinye. Kungenzeka ukuthi unike leli tafula igama elilula njenge "Amanani."
Mhlawumbe ufuna ukukhipha izinto ezisitolo sakho ezithengwa ngaphezu kuka-$ 25, "ubuza" imininingwane yedatha yazo zonke lezi zinto. Yilapho i-SQL ingena khona.
Umbuzo wakho Wokuqala we-SQL
Ngaphambi kokuba singene esitatimendeni se-SQL esidinga ukubuyisa lolu lwazi, ake sizame ukuqeda umbuzo wethu ngesiNgisi esicacile. Sifuna "ukhethe zonke izinombolo zesitoko kusukela kuthebula lamanani lapho intengo idlula u-$ 25." Lesi sicelo esihle kakhulu uma siboniswa ngesiNgisi esicacile, futhi cishe siselula ku-SQL. Nasi isitatimende esifanayo se-SQL:
Khetha isamba seStock
KUSUKA Amanani
LAPHO Inani> 5
Kulula njengaleyo! Uma ufunda isitatimende ngenhla ngokuzwakalayo, uzothola ukuthi ufana kakhulu nombuzo wesiNgisi esiwubeke esigabeni sokugcina.
Ukuhumusha izitatimende ze-SQL
Manje ake sizame esinye isibonelo. Lesi sikhathi, noma kunjalo, sizokwenza emuva. Okokuqala, ngizokunikeza isitatimende se-SQL futhi ake sibone ukuthi ungayichaza ngesiNgisi esilula:
Khetha inani
KUSUKA Amanani
LAPHO I-StockNumber = 3006
Ngakho, ucabanga ukuthi lesi sitatimende senzani? Kulungile, ithola intengo kusuka ku-database yento engu-3006.
Kukhona isifundo esisodwa esilula okufanele ususe ekuxoxweni kwethu kuleli phuzu: I-SQL ifana nesiNgisi. Ungakhathazeki ngokuthi ungakha kanjani izitatimende ze-SQL; sizofinyelela kulowo wonke uchungechunge lwethu. Vele uqaphele ukuthi i-SQL ayikwesabisi njengoba ingase ivele kuqala.
I-Range yeSitatimende SQL
I-SQL inikeza ububanzi obukhulu bezitatimende, okukhethwa kuzo okulodwa. Nazi ezinye izibonelo zezinye izitatimende ezijwayelekile ze-SQL:
- I-SQL INSERT ne-SQL DELETE: Ukufaka noma okususa irekhodi etafuleni
- I-SQL UPDATE: Iguqula amarekhodi etafuleni
- I-SQL CRELE ne-SQL DROP: Yakha noma isusa ithebula
Ngaphandle kwalezi zitatimende ze-SQL, ungasebenzisa izigaba ze-SQL, phakathi kwazo isigatshana se-WHERE esisetshenziswe kwizibonelo zangaphambilini. Lezi zigaba zisebenza ukucubungula uhlobo lwedatha ukuze lisebenze. Ngaphandle kwesigatshana se-WHERE, nansi amanye amagatshana asetshenziswa kakhulu:
- KANYE NOMA KANYE: Hlanganisa izimo eziningi ukuze ulungise isitatimende se-SQL
- NJENGOBA: Uqhathanisa ukubaluleka kwamanani afanayo usebenzisa i-wildcard
- UKUQALA: Uhambisa idatha ekhuphuka noma ehlehla
Uma unesithakazelo ekuqhubekeni okuqhubekayo nokuhlola i-SQL, i- SQL Okubalulekile kuyisifundo esiyingxenye ehlukahlukene esihlola izingxenye nezici ze-SQL ngokuningiliziwe.