Kuxazululiwe: khetha imigqa eyi-10 yokuqala

I-Oracle SQL isivumela ukuthi sisebenzise futhi siphathe idatha kusizindalwazi esihlobene. Imisebenzi evamile ihlanganisa ukubuza idatha, ukudala amathebula, nokuthuthukisa izinqubo zokucubungula idatha eziyinkimbinkimbi. Umsebenzi owodwa ovamile ofezwa onjiniyela nge-SQL ukukhetha imigqa ethile kuthebula lesizindalwazi. Kwesinye isikhathi, kungase kudingeke ukuthi sikhawulele ukuthi mangaki amarowu esiwakhethayo, ngokuvamile ngenxa yezizathu zokusebenza. Ngokuzenzakalelayo, uma ubhala isitatimende "KHETHA" ku-Oracle SQL, sithola yonke imigqa kuthebula eliqokiwe elihlangabezana nemibandela yakho. Kodwa kuthiwani uma sifuna kuphela imigqa eyi-10 yokuqala? Kulo mhlahlandlela, sizobonisa indlela yokukhetha kuphela imigqa yokuqala eyi-10 ku-Oracle SQL.

KHETHA *
KUSUKA (KHETHA *
KUSUKA etafuleni_lakho
UKUHLELA NGEkholomu_ ethile)
LAPHO ROWNUM <= 10; [/ikhodi]

I-Oracle SQL isebenzisa ikholomu-mbumbulu ekhethekile ebizwa ngokuthi โ€œROWNUMโ€ ukuvumela abathuthukisi ukuthi benze imisebenzi efana nale. Le kholamu mbumbulu isinika inombolo yomugqa ngamunye uma ibuyiswa, iqala ku-1 ikhuphuke iye kuye ngokuthi miningi kangakanani imigqa embuzweni.

Incazelo yekhodi enemininingwane

Ake sihlaziye ukuthi lo mbuzo usho ukuthini.

[ikhodi lang=โ€Oracle SQLโ€]
KHETHA * KUSUKA (KHETHA * KUSUKA_KOKUHLELA KWETHEBULA LAKHO NGEkholomu_ ethile)

Le ngxenye yokuqala yombuzo ikhetha wonke amakholomu kuthebula lakho bese iwahlunga ngokuthi โ€œikholomu_elithileโ€. Siyayihlunga ngoba i-ROWNUM yabelwa imigqa ngemva kokuhleleka ngesigatshana nangaphambi kwanoma yikuphi ukuhlunga ithatha indawo.

LAPHO ROWNUM <= 10; [/code] Ingxenye yesibili yombuzo yilapho ikholomu mbumbulu ethi "ROWNUM" iqala ukusebenza khona. Itshela i-Oracle ukuthi isinike kuphela imigqa lapho i-ROWNUM iyi-10 noma ngaphansi, ngakho-ke, imigqa yokuqala eyi-10. Inothi elilodwa eliyisihluthulelo lapha ukuthi amanani angu-ROWNUM abelwa emigqeni ebuyisiwe kusukela ku-1 futhi amanani awazibophezeli kuze kube ngemva kokuba isigatshana esithi "ORDER BY" sesicutshungulwe ngokugcwele.

ROWNUM kanye nokusebenza

Ukusebenzisa ROWNUM ingathuthukisa kakhulu ukusebenza, ikakhulukazi uma usebenzisana nenani elikhulu ledatha. I-Oracle akudingeki ilande yonke idatha kudiski futhi iwabambe ekhanda ngaphambi kokuthi iqale ukubuyisela imiphumela. Ingakwazi ukubuyisela imiphumela ngokushesha nje lapho ithola eyokuqala eyi-10 egcwalisa zonke izimo kumyalo we-SQL.

Imisebenzi efanayo

Umsebenzi ofanayo ne-ROWNUM ku-Oracle SQL ngu LANDA OKOKUQALA n IMIGQA KUPHELA. Nokho, lesi sigatshana somthetho sitholakala kuphela ku-Oracle 12c nezinguqulo zakamuva.

[ikhodi lang=โ€Oracle SQLโ€]
KHETHA *
KUSUKA etafuleni_lakho
UKUHLELA NGEkholomu_ ethile
LANDA IMIGQA EYI-10 KUPHELA;

Sekukonke, i-Oracle SQL ihlinzeka abahleli bohlelo ngamasu ambalwa awusizo ukuze bakhawulele inani lemigqa ebuyiswa ngombuzo othi KHETHA.

Okuthunyelwe okuhlobene:

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