Ukubuyisa Idatha Evela Emathebula Amaningana Ngezihlanganisi Zangaphakathi SQL

I-Inner ijoyina imininingwane yokubuyisela evela kumininingwane yolwazi emibili noma ngaphezulu

Ukujoyina kwangaphakathi ukujoyina okujwayelekile kakhulu ku-SQL. Babuyela kuphela ulwazi olukhona amatafula amabili noma ngaphezulu. Isimo sokujoyina sinquma ukuthi yimaphi amarekhodi ahlanganiswe ndawonye futhi achazwe kusigaba somthetho. Isibonelo, uma udinga uhlu lwamathiphu omshayeli / imoto lapho imoto kanye nomshayeli ekhona edolobheni elifanayo, umbuzo olandelayo we- SQL ufeza lo msebenzi:

HLOLA igama lokugcina, igama lokuqala, umaki KUSUKA abashayeli, izimoto NOMA lapho abashayeli.wahlukaniswa = izimoto

Nazi imiphumela:

igama lokugcina igama lomsebenzisi
----------- ------------ ----
Baker Roland H122JM
Smythe Michael D824HA
Smythe Michael P091YF
Jacobs Abraham J291QR
Jacobs Abraham L990MT

Qaphela ukuthi imiphumela yikho kanye eyayifunwa. Kungenzeka ukuthi uthuthukise umbuzo ngokucacisa izinkombandlela ezengeziwe kwi-WHERE clause. Cabanga ukuthi imingcele yokuqala yombuzo ihambisana nabashayeli bezimoto ezingagunyaziwe ukushayela (abashayeli bamaloli emotweni nakwezinye izinto). Ungasebenzisa umbuzo olandelayo ukuxazulula le nkinga:

Khetha igama lokugcina, igama lokuqala, ithegi, izimoto.class KUSUKA abashayeli, izimoto NAKHO lapho abashayeli.location = izimoto.wahlukaniswa NABASEKHANDI.class = izimoto.class

Lesi sibonelo sicacisa ithebula elisuka embonweni weklasi kusigaba se-SELECT ngoba isigaba singenangqondo-sibonakala kuzo zombili amatafula. Ikhodi ngokuvamile izocaca ukuthi ikholomu yiphi itafula kufanele ifakwe emiphumeleni yombuzo. Kulesi simo, akwenzi umehluko, njengoba amakholomu afana futhi ajoyine esebenzisa i-equijoin. Noma kunjalo, uma amakholomu enemininingwane ehlukile, lokhu kuhlukaniswa kuyoba okubalulekile. Nanka imiphumela yalo mbuzo:

Igama lokugcina lomkhakha wethegi
---------- ------------ ---- ------
I-Baker Roland H122JM Imoto
Smythe Michael D824HA Truck
Jacobs Abraham J291QR Imoto

Imigqa elahlekile yabhanjiswa uMichael Smythe emotweni kanye no-Abraham Jacobs eya emotweni, izimoto ezazingagunyaziwe ukushayela.

Ungasebenzisa futhi ukujoyina kwangaphakathi ukuhlanganisa idatha kusuka kumatafula amathathu noma ngaphezulu .