Umsebenzi wokudala itafula ku-SQL - Dala ithebula

Ukusebenza nolwazi oluhlobene nolwazi luhlobene ngqo namatafula ashintshayo kanye nedatha equkethwe kuwo. Kodwa ngaphambi kokuqala kwesenzo, itafula kufanele lenziwe. Ukuzenzekelayo le nqubo, kukhona umsebenzi okhethekile we-SQL obizwa ngokuthi "CREATE TABLE".

Into yokuqala!

Ngaphambi kokubhekana nenqubo yokudala amathebula usebenzisa umyalo we-MS SQL "YADALA ITHEBULA", kuyakudingeka ukuhlala kulokho okudingeka ukwazi ngaphambi kokusebenzisa lo msebenzi.

Okokuqala, udinga ukuza negama letafula - kumele libe yinto ehlukile, uma kuqhathaniswa nabanye, elise database, bese ulandela imithetho eminingana. Igama kumele liqale ngencwadi (az), emva kwalokho noma yiziphi izinhlamvu, izinombolo kanye nokubeka phambili okulandelayo kungalandela, futhi inkulumo elandelako akufanele ibe yigama eligcinwe. Ubude begama letafula alikwazi ukudlula izinhlamvu ezingu-18.

Ngemuva kokuchaza igama, kufanele uhlakulele isakhiwo: cabanga ngamagama amakholomu, ucabange ngohlobo lwedatha esetshenziselwa kubo, nokuthi yiziphi izinkambu okumelwe zigcwaliswe. Lapha kufanele ngokushesha ubone izinkambu zangaphandle zangaphandle neziyisisekelo, kanye nemikhawulo engenzeka yamanani wedatha.

Ama-nuances asele etafuleni angalungiswa kalula, ngakho esiteji sokudala itafula, angacatshangwa ngokungagcini ngokuphelele.

I-Syntax

Ngemva kokuthuthukisa isakhiwo setafula, ungaqhubeka ukuyidala. Ukwenza lokhu kulula, usebenzisa umsebenzi we-SQL "DALA ITHEBULA". Kulo, umsebenzisi kudingeka ukuba acacise igama lethebula lesakhelwe ngaphambili kanye nohlu lwamakholomu, ecacisa uhlobo kanye negama ngayinye yazo. I-syntax yomsebenzi ilandelayo:

DALA ITHEBULA lesitayela sethebula
({I-column_name datatype [inkulumo DEFAULT] [ikholomu_constraint] ... | table_constraint}
[, {Idatha yamagama ekholomu_name [DEFAULT expression] [ikholomu_constraint] ... | I-Table_constraint}] ...)

Iziphakamiso ezisetshenziselwa ukwakhiwa komsebenzi zisho lokhu okulandelayo:

• Ithebula_name - igama lethebula
• Ikholomu_magama yigama lekholomu
• I-Datatype iyinhlobo yedatha esetshenziswe kule nsimu
• DEFAULT yiyona inkulumo esetshenziswe kukholomu ezenzakalelayo.

Kungenzeka futhi ukusebenzisa ezinye izimpikiswano ezimbili zomsebenzi:

• I-Colum_constraint - imingcele yekholomu
• Ithebula_constraint - imitha yemingcele

Kuzo, umsebenzisi angacacisa imingcele edingekayo noma izimo zokugcwalisa itafula.

Izici zokudala amatafula

Lapho ubhala umbuzo nomsebenzi we-SQL "DALA ITHEBULA", ngezinye izikhathi udinga ukusetha imithetho yokugcwalisa amasimu. Ukuze wenze lokhu, engeza izimfanelo ezikhethekile zomsebenzi ochaza eyodwa noma enye isethi yemibandela.

Ukuze unqume ukuthi inani elingenalutho litholakala esitokisini, ngemuva kokucacisa igama kanye nohlobo lwekholomu, elinye lamagama angukhiye e-NULL (angase abe ngamanani angenamkhawulo) noma AKUKHO NULL (insimu kumele igcwaliswe) kufanele ibhaliswe.

Uma udala itafula ezimweni eziningi, kuyadingeka ukuthi uhlanganise ubunye bokungena ukuze ugweme ukutholakala kokubili okufanayo. Kulokhu, ukubalwa kwemigqa kuvame ukusetshenziswa. Futhi, ukuze ungadingi umsebenzisi ukwazi inombolo yokugcina etholakalayo etafuleni, emsebenzini "DALA ITHEBULA" kunele ukucacisa ikholomu yekhiye eyinhloko ngokubhala igama elingukhiye "Ukhiye oyinhloko" ngemuva kwensimu ehambelanayo. Ngokuvamile, kuyisihluthulelo esiyinhloko esixhuma amathebula komunye nomunye.

Ukuze unikeze isixhumanisi kukhiye oyinhloko, impahla yesihluthulelo sangaphandle "ISIKHATHI SOKUPHUMA" sisetshenziswa. Ngokucacisa le ndawo yekholomu, ungaqiniseka ukuthi le nsimu iqukethe inani elifana nelinye lalabo abatholakala kukholomu eyinhloko yekholomu efanayo noma enye ithebula. Ngale ndlela, ungaqinisekisa ukuthi idatha ayinjalo.

Ukuqinisekisa ukuhambisana nesethi enikeziwe noma incazelo, sebenzisa i-CHECK imfanelo. Kubhaliwe ekugcineni ohlwini lwezingxabano kulo msebenzi futhi kunemibono enengqondo njengeparitha yomuntu siqu. Ukusebenzisa, ungakwazi ukukhawulela uhlu lwamanani angenzeka, isibonelo, usebenzisa kuphela amagama "M" no- "F" emkhakheni wetafula "Ubulili".

Ngaphezu kokunikezwayo, umsebenzi we-SQL "DALA ITHEBULI" unezimfanelo eziningi eziqondile, kodwa zisetshenziselwa ukwenza okuningi kakhulu.

Izibonelo

Ukuze uqondisise ngokugcwele isimiso somsebenzi, kubalulekile ukucabangela ngokusemthethweni ukuthi UKUSHILE ITHEBULA (SQL) kusebenza kanjani. Isibonelo esingezansi sidala itafula eliboniswe kulolu hlobo:

DALA ITHEBULI Ngokwezifiso
(ID CHAR (10) AKUKHO NULL Ukhiye oyinhloko,
I-Custom_name CHAR (20),
I-Custom_address CHAR (30),
I-Custom_city CHAR (20),
I-Custom_Country CHAR (20),
I-ArcDate CHAR (20))

Njengoba ungabona, ipharamitha yokungabikho kwenani eliselikilini (NULL) ingasuswa, ngoba isetshenziswe ngokuzenzakalelayo.