I SQL yam khetha khetha: umsebenzisi isampulu

I SQL yam, njengayo nayiphi na inkqubo yolawulo ledatha ezinobume, uye kubume bayo isampuli ingxelo KHETHA. Akumangalisi oku, kuba iinkcukacha eziqulathe ulwazi oluyimfihlo ngokuyintloko ukuyibuyisa xa kuyimfuneko. select from SELECT позволяет делать это множеством различных способов, предоставляя большой набор инструментов. I SQL yam khetha ukusuka KHETHA ingxelo likuvumela ukuba wenze oku ngeendlela ezininzi ezahlukeneyo, ngokubonelela okukhulu yezixhobo.

MySQL ukufaka

I SQL yam iqalisa njengoko phantsi Windows, yaye phantsi kwe Linux. Ukufakela I SQL yam Ubuntu, enze amaqela amabini ngokufanelekileyo xa ukuphela kwe OS;

- Sudo apt-ukufumana ukufaka mysql-server.

- Sudo apt-ukufumana ukufaka mysql-client.

For I SQL yam Windows, khuphela nje ukusuka kwisayithi esemthethweni "database" iiphakheji ezifanelekileyo ufakelo aze asebenze.

Kumbutho we kwingxelo KHETHA

Zalisa isakhiwo I SQL yam khetha ukusuka ingxelo KHETHA ngolu hlobo lulandelayo:

1. KHETHA - amagama column (fields).

2. FROM - itafile amagama.

3. APHO - yimeko apho isampula.

Qaphela ukuba lo gama lwesivakalisi SQL ulwimi ayikho case-sensitive, umkhwa elungileyo ukubhala iingxelo kunye amagama eli phepha (FROM, PHI, njl) ngoonobumba abakhulu, kunye namagama iitafile kunye kwiikholam - encinane. SELECT приведен на рисунке ниже. Owona mzekelo elula yokusebenzisa umqhubi I SQL yam khetha ukusuka KHETHA eboniswe ngezantsi.

Asterisk emva ilizwi KHETHA i-analogue le igama BONKE kuthetha ukuba ukususela itafile inikwa ukhethe yonke imihlathi. Ukuba unomdla kuphela kwezinye ingentsimi etafileni, kufuneka kuboniswe kwindawo efanelekileyo, wodwa ngeziphumlisi. Kukwasebenza kwanjalo kuyo amagama iitafile - Ukuba ngaphezu kwesinye, angene kubo bonke wodwa ngeziphumlisi.

Ukusebenzisa KUPHI

Licacile elokuba, ukuba akwazi ukunceda, kodwa uphawula ukuba kulo mzekelo hundzeke, akukho igama APHO - oku kungenxa kule meko ke asimele. asifuneki Le ngxelo, nakubanini ozikhethelayo hlobo KHETHA, baninzi, kodwa kancinci kamva. Ukuba emva igama lidibanisa i itafile PHI kunye nayiphi na imeko, ezifana type = 'inja', ngoko ke iseti umphumo uya kufumana kumqolo omnye kuphela pet egameni Edison. Lo mzobo ungezantsi ubonisa umzekelo. Musa Ziba ingxelo UKUZE YI, apha akunamsebenzi, kwaye oko kuya kuxoxwa kancinane emva koko.

Kubalulekile ukuphawula ukuba emva kokuba UPHI kwakhona kuyenzeka ukuba babhale iimeko ezininzi, kodwa akusayi wodwa ngeziphumlisi. Ukulungiselela le njongo, kufuneka usebenzise amagama afana KUNYE okanye OKANYE. konke kuxhomekeke kwindlela kufuneka kuhlangatyezwane neemeko zakho. Ukuba unomdla yoko okwanelisa zonke iimeko ucacise, ngoko phakathi kwabo kufuneka KUNYE, ukuba umphumo kufuneka zanelise ubuncinane omnye kubo, ngoko sebenzisa i-OR.

UKUZE BY igatya

Sathi sakuchaza ukuba ukongeza APHO kwingxelo KHETHA kukho ezinye amagama ezininzi apho ukwazi ukwqhatha iziphumo ezibekwe njengoko kuyimfuneko kwimeko ethile. Omnye "izitshixo" na UKUZE BY. It ikuvumela ukuba ukubeka iziphumo isampuli ngaphakathi kwinkalo ethile, zombini zinyuka zisihla. Akwanelanga ukuba ucacise nje igama umhlathi emva kwakhe, ngokutsho iinqobo ekufuneka ukuyisombulula le data. Kubalulekile ukuba ukuthobela imiqathango ezininzi: eyokuqala - igama echazwe kwingxelo, UKUZE YI, yaye kufuneka ibe khona kwi KHETHA; yesibini - UMYALELO BY kufuneka ibekwe ekupheleni isicelo.

Uhlobo Ngokungagqibekanga unyukela (ASC), kodwa ukuba ufuna ukubeka iziphumo kwehle, bhala emva igama intsimi endaweni ASC elingundoqo DESC.

isiphelo

Siye kwakhona omkhulu, kodwa hayi zonke izixhobo umqhubi I SQL yam ukhethe ukusuka. KHETHA, ngaphandle kwezo zikhankanywe ngasentla, has a lot of ezinye iimpawu evumela ukuba kuvunjululwe idata esuka ledatha, evumayo efanelekileyo.