KOKUBA SQL: incazelo, miyalelo, izibonelo

SQL siwulimi ejwayelekile ngokusebenzisana yolwazi zingubudlelwane. Anakho ekuchithweni kwayo iqoqo amathuluzi anamandla for ukuxhaphaza idatha egcinwe kwi-amatafula.

Ngokungangabazeki, ikhono idatha iqembu isampula zabo nsuku ethize ingenye ithuluzi enjalo. SQL sitatimende KOKUBA kanye LAPHO umshwana ikuvumela ukuba ukuchaza izimo isampula baye babeqoqana idatha ngandlela-thile.

Sepharamitha SQL KOKUBA: Incazelo

Okokuqala kuyinto ephawulekayo ukuthi lo mshumayeli ipharamitha kungakhethwa, futhi isetshenziswa kuphela ngokuhlangana ne-GROUP BY inketho. Njengoba khumbula, GROUP BY isigatshana isetshenziswa lapho KHETHA isebenzisa imisebenzi aggregate futhi imiphumela ukubalisisa kwabo ukuze uthole amaqembu athile. Uma LAPHO ikuvumela ukuba ucacise izimo Ukukhetha phambi idatha babeqoqana, le KOKUBA unamalungiselelo emayelana kakade ngqo amaqembu ngokwabo. Ukuze uthole ukuqonda kangcono, ake udabule isibonelo kohlelo okwethulwa kulo mdwebo ongezansi.

Lena isibonelo esikhulu sokupha KOKUBA incazelo SQL. Ingabe itafula nge uhlu lwamagama imikhiqizo, izinkampani esikhiqiza kubo, futhi abanye nakweminye imikhakha. Umbuzo in the eliphezulu ngakwesokudla ekhoneni, sizama ukuthola ulwazi bangaki izinhlobo zemikhiqizo inkampani ngayinye silwenza, futhi umphumela waba ukuthi sifuna ukubonisa kuphela lezo zinkampani ukuthi likhiqize izinhlobo ezingaphezu kuka-2 izinto. kwakhiwa GROUP BY ndlela amaqembu amathathu elihambisana amagama ezinkampani, ngamunye okuyinto eye zathi isibalo sezincwadi imikhiqizo (imigqa). Kodwa ukubeka KOKUBA isimo gumbi iqembu okukodwa isampuli okuholela, ngoba onganelisekile isimo. Ngenxa yalokho, sithola amaqembu amabili elihambisana inani izinkampani ezikhiqizayo 5 no-3.

Noma nini kungase kuphakame Umbuzo ukuthi kungani ukusebenzisa KOKUBA, uma kukhona SQL LAPHO. Uma thina wasebenzisa LAPHO, wayezobe wabheka lonke inani lemigqa itafula, kunokuba ngamaqembu, isimo Bekuyoba ukungabi nangqondo kuleli cala. Nokho, ngokuvamile i-bangakwazi ukuhlala ndawonye nombuzo owodwa.

Kusibonelo esingaphezulu singabona kanjani ekuqaleni kukhona Ukukhetha idatha egameni umsebenzi elicacisiwe ipharamitha LAPHO, bese eqenjini GROUP BY yi is ngaphezu kwalokho ihlolwe ngu isamba iholo lomsebenzi ngamunye.

Sepharamitha SQL KOKUBA: izibonelo, le-syntax

Cabangela ezinye izici KOKUBA SQL-syntax. Incazelo yaleli ipharamitha ulula. Okokuqala, njengoba sekuphawuliwe kakade, isetshenziswa kuphela ngokuhlangana ne-GROUP ipharamitha BY futhi wabonisa ngokushesha ngemva kwalokho futhi ngaphambi ORDER BY, uma ekhona isicelo. Kuyaqondakala, kusukela KOKUBA inquma imibandela idatha kakade babeqoqana. Okwesibili, isimo sale ipharamitha imisebenzi aggregate kuphela ingasetshenziswa nasemasimini ezisohlwini ipharamitha GROUP BY. Zonke izimo kuleli ipharamitha wabonisa ngendlela efanayo njengoba kwaba njalo endabeni ka-WHERE.

isiphetho

Njengoba ubona, lutho nzima kulesi sitatimende ungapheli. Wokufihla, isetshenziswa ngendlela efanayo njengoba LAPHO. Kubalulekile ukuqonda ukuthi usebenzisa LAPHO kuwo wonke idatha ekhethiwe futhi KOKUBA - kuphela mayelana namaqembu kuchaziwe GROUP ipharamitha BY. Sethule incazelo olunzulu KOKUBA SQL, okuyinto kwanele ukuze iphatheke beqiniseka.