KOKUBA SQL: inkcazelo, syntax, imizekelo

SQL lulwimi eqhelekileyo yokusebenza zolwazi zonxulumelwano. Lowo unayo yayo ngothotho lwezixhobo ezinamandla lokuhanahanisa i data agcinwe ezitafileni.

Alithandabuzeki elokuba, ukukwazi data iqela kwisampulu zawo zovavanyo rhoqo ethile yenye yezo isixhobo. Ingxelo SQL KOKUBA kunye APHO igatya ikuvumela ukuba ukuchaza imiqathango isampuli azibeke idata ngandlel 'ithile.

Ipharamitha SQL KOKUBA: Inkcazelo

Okokuqala kubalulekile ukuqaphela ukuba le parameter ungayikhetha, kwaye isetyenziswa kuphela xa kubanjiswene ne GROUP BY ukhetho. Njengoko khumbula, GROUP BY gatya kusetyenziswa xa kwi KHETHA isebenzisa imisebenzi aggregate yaye iziphumo ubalo zabo ukuya kumaqela athile. Ukuba UPHI ikuvumela ukuba ukhankanye iimeko ukhetho phambi kokuba i data ngokwamaqela, nokuba iqulethe imiqathango emalunga data sele ngqo kumaqela ngokwabo. Kuba ukuqonda ngcono, masihambe esebenzisa njengomzekelo inkqubo thaca kulo mzobo ungezantsi.

Lo ngumzekelo enkulu yokunika KOKUBA inkcazo SQL. Ngaba itafile uluhlu lwamagama iimveliso, iinkampani ezivelisa nabo, kunye namanye amacandelo. Lo umbuzo kwi ephezulu kwikona lasekunene-lesandla, sizama ukufumana ingcaciso emalunga nokuba zingaphi iindidi zemveliso yenkampani nganye utywala, kunye result ukuba sifuna ukubonisa kuphela ezo iinkampani ezivelisa izinto ezingaphezulu kwama-2. IQELA BY khetho ukusekwa amaqela amathathu ehambelana amagama eenkampani nganye ethe Ababalwayo kubo ngenani lawo iimveliso (imiqolo),. Kodwa ukubeka yakho KOKUBA imeko gumbi iqela elinye kwisampula onesiphumo, ekubeni akukho ukwanelisa imeko. Ngenxa yoko, sifumana amaqela amabini ehambelana inani kwiinkampani zemveliso 5 no-3.

Lo mbuzo esinokubakho ukuba kutheni ukusebenzisa KOKUBA, ukuba kukho SQL APHO. Ukuba wasebenzisa APHO, ange wajonga inani lemiqolo unabo, kunokuba bengamaqela, kwaye imeko ongamenzanga ingqondo kule meko. Noko ke, ngokufuthi aphile kunye umbuzo omnye.

Kulo mzekelo ungentla sinokubona indlela kwi kuqala na ukhetho lwe data egameni umqeshwa okhankanywe apho parameter, uze emva koko ngokwamaqela kwi GROUP BY Umphumela Ukongezelela sivavanywe sum of kumvuzo ngomqeshwa ngamnye.

Ipharamitha SQL KOKUBA: imizekelo, kwezivakalisi

Cinga ezinye iimpawu KOKUBA SQL syntax. Inkcazelo yale parameter ilula. Okokuqala, njengokuba sele kukhankanyiwe, isetyenziswa kuphela ngokusebenzisana kunye parameter GROUP BY waza wabonisa ngoko nangoko emva koko naphambi UKUZE YI, xa ekhona isicelo. Iyaqondakala, ekubeni KOKUBA imisela imiqathango ye data esele ngokwamaqela. Okwesibini, xa imeko yale parameter kuphela imisebenzi aggregate zingasetyenziswa kunye namasimi ezidweliswe kwi parameter GROUP BY. Zonke iimeko kule parameter kuboniswe ngendlela efanayo xa APHO.

isiphelo

Njengoko ubona, akukho nto nzima kule ngxelo musa. Semantically, lisetyenziswa ngendlela efanayo njengoko KUPHI. Kubalulekile ukuqonda ukuba ukusebenzisa APHO kuzo zonke data ezikhethiweyo kwaye KOKUBA - kuphela ngokuphathelele kumaqela ezichazwe kwi parameter GROUP BY. Savelisa inkcazelo ebanzi ngokuba SQL, nto leyo kwanele ukuba ukuphathwa siqinisekile.