SQL "ngoba Dummies": lokho odinga ukukwazi imfundamakhwela?

Kuze kube manje, "for dummies" izifundo SQL ayabaluleka kuthandwa. Kungaba lula kakhulu ukuchaza, ngoba ezikhathini eziningi ungathola okuthiwa "ashukumisayo" amasevisi wewebhu emhlabeni namuhla. Beqi- emgodleni nezimo futhi zisekelwe yolwazi. Zonke program imfundamakhwela abaye yanquma azinikele ukudalwa amasayithi, ngokuyinhloko yalotshelwa ukunikeza izifundo SQL "for dummies".

Kungani ukufunda ulimi?

Okokuqala, SQL lufundiswe ukuze ukuze uyothuthukisa ukudalwa ezihlukahlukene izicelo omunye ethandwa kakhulu kuze kube manje izinjini namabhulogi - WordPress. Ngemva kokudlula ezikhungweni Ezifundweni ezimbalwa ezilula, ngeke vele ukwazi ukudala imibuzo yimuphi yinkimbinkimbi, okufakazela inkimbinkimbi ulimi kuphela.

Kuyini SQL?

Ulimi Lokusebenza Oluhlelekile, noma Ulimi Lokusebenza Oluhlelekile, sidalwe nomunye injongo eyodwa: ukucacisa uhlobo idatha, ukuhlinzeka ukufinyelela kuwo futhi sibaphathe ngendlela ngezikhawu esifushane. Uma wazi SQL-value-ke wenza kanjalo uyokuqonda ukuthi kule seva kungokwalabo okuthiwa izilimi "nonprocedural". Okungukuthi ikhono layo ukufaka kuphela incazelo yanoma iyiphi izingxenye noma imiphumela ufuna ukubona esikhathini esizayo kusayithi. Kodwa lokhu uMklami alisho ngalokho ncamashi uya uthole imiphumela. isicelo ngasinye esisha ngalolu limi uhlobo extra "superstructure." Kuleso ngokulandelana kwazo zifakiwe database, nezicelo iyofezeka.

Yini izinqubo engenziwa usebenzisa lolu limi?

Naphezu alula, SQL egciniwe ikuvumela ukudala eziningi izicelo onhlobonhlobo. Ngakho yini ongayenza uma sifunde lolu limi izinhlelo ezibalulekile?

• ukudala ezihlukahlukene amatafula;
• ukuthola, esitolo, futhi ukushintsha idatha;
• Ukushintsha isakhiwo amatafula kwalo yedwa;
• sihlanganise ulwazi wathola ukuze zibe yisikhungo esisodwa;
• ukubala idatha etholakele;
• ukunikeza isivikelo egcwele ulwazi.

Yikuphi amaqembu athandwa kakhulu kulolu limi?

Uma unquma ukuvakashela izifundo SQL "for dummies" ke uzothola ulwazi lemininingwane mayelana nokuthi imiyalo ezisetshenziswa ekwakheni imibuzo ngayo. Okuvame kakhulu kude zimi kanje:

1. DDL - kuba umyalo elicacisa idatha. It isetshenziswa ukudala, shintsha futhi ususe tintfo letehlukene database.
2. DCL - iqembu ephethe idatha. Isetshenziselwa ukunikeza ukufinyelela abasebenzisi ezahlukene ulwazi egciniwe, kanye ukusebenzisa ithebula noma umbono.
3. TCL - iqembu ephethe izinhlobo ezihlukahlukene zezindwangu ezingaba ukuthengiselana. Injongo yayo oyinhloko ukucacisa Yiqiniso kuthengiselana.
4. DML - manipulates idatha etholwe. Injongo yalo uvumela umsebenzisi ukuhambisa ezihlukahlukene ulwazi kusukela database noma nomthelela.

Izinhlobo amalungelo ezikhona kule seva

Ngaphansi ilungelo libhekisela lezo zenzo okungase enze elilodwa noma omunye umsebenzisi ngokuvumelana isimo sabo. Ephansi Yiqiniso, kuyinto ngemvume evamile. Yiqiniso, ngokuhamba kwesikhathi amalungelo iyashintsha. Old kuzosuswa futhi abasha wanezela. Kusukela namuhla, zonke abadlula SQL Server izifundo "for dummies", ukwazi ukuthi kukhona izinhlobo eziningana imisebenzi kuvunyelwe:

1. Lwento - umsebenzisi ovunyelwe ukwenza noma yimuphi umyalo kuphela maqondana into ethile okungukuthi database. Ngesikhathi esifanayo izinto ezingefani amalungelo ehlukene. Futhi enamathiselwe hhayi kuphela umsebenzisi othile, kodwa futhi amatafula. Uma omunye usebenzisa amakhono abo, Ngazakhela etafuleni, bese-ke ubhekwa umnini wayo. Ngakho-ke, ngo-ilungelo lakhe ezomisa amalungelo entsha abanye abasebenzisi ezihambisana ngolwazi kuwo.
2. System Uhlobo - okubizwa ngokuthi ulwazi lwe-copyright. Amakhasimende abathola amalungelo anjalo, ungakha ezihlukahlukene izinto database.

Umlando SQL

Lolu limi sidalwe IBM ngo-1970, i-laboratory ucwaningo. Nakuba igama lakhe kwakunguJohane ukuhluka (kumdlalo), kodwa ngemva kweminyaka embalwa ukusetshenziswa, washintsha, ukunciphisa kancane. Naphezu kwakho konke lokhu, ngisho nanamuhla, abaningi ochwepheshe international owaziwa emkhakheni lwezinhlelo namanje amemezele igama elidala. SQL wadalwa ngenjongo eyodwa - baziqambela ngolimi bekuyoba lula ukuze ayengakwenza ngaphandle kwezinkinga ukufunda ngisho elula abasebenzisa i-Internet. Kuvele Eqinisweni ezithakazelisayo wukuthi ngesikhathi SQL wayengeyena ulimi enjalo kuphela. Ngo California, elinye iqembu lezazi uye wazakhela Ingres efanayo, kodwa akazange zande. Kuze kube ngo-1980, lapho Kwakuhlukahluka eziningana SQL, okuyizinto kuphela ngokwezinga elithile sihluke nomunye. Ukuvimbela ukudideka, ngo-1983, i-okufana ejwayelekile sidaliwe, okuyinto ethandwa namuhla. SQL izifundo "ngoba Dummies" ukukwazisa okuningi mayelana isevisi kanye ngokugcwele wuhlole amasonto ambalwa.