Amandla wezinkinobho zangaphandle ezigciniwe ezihlobene

Isihluthulelo sangaphandle sivula umnyango wezwe lonke lemininingwane

Abaqambi be-database basebenzise ngokubanzi izihluthulelo lapho bethuthukisa ulwazi oluhlobene nolwazi. Phakathi kwalezi zihluthulelo ezivame kakhulu izihluthulelo eziyisisekelo nezikhiphe zangaphandle. Isihluthulelo sangaphandle sedatha yinkambu etafuleni elihlobeneyo elifana nekholomu eyinhloko yekholomu enye ithebula. Ukuze uqonde ukuthi ikhi langaphandle lisebenza kanjani, ake sihlolisise umqondo wedatha yokuxhumana.

Ezinye Eziyisisekelo Ezigciniwe Ezihlobene

Esikhathini sedatha yokuxhumana, idatha igcinwa kumatafula aqukethe imigqa namakholomu, okwenza kube lula ukucinga nokuphatha.Kukhona izibalo ezingathí sina ngemuva komqondo wedatha yokuxhumana (i-algebra ehlobene, ehlongozwa yi-EF

I-Codd ku-IBM ngo-1970), kodwa akusiyo isihloko salesi sihloko.

Ngezinhloso ezingokoqobo (nabangewona wezibalo), i-database yokuxhumana igcina imininingwane "ehlobene" emigqa namakholomu. Okuqhubekayo-futhi lapha yilapho ithola khona okuthakazelisayo-yolwazi oluningi lwakhiwe ukuze idatha etafuleni elilodwa ikwazi ukufinyelela idatha kwelinye itafula. Lekhono lokudala ubuhlobo phakathi kwamatafula yiwona amandla langempela yedatha yokuxhumana.

Ukusebenzisa ama-Keys angaphandle

Amatafula amaningi, ikakhulukazi kulawo maqondana amakhulu, anesibindi, anezihluthulelo eziyisisekelo. Amathebula aklanyelwe ukufinyelela amanye amatafula kumele abe nesikhiye sangaphandle.

Ukuze usebenzise idatha ejwayelekile ekhonjiwe yaseNorthwinds, nansi inkinga evela kuthebula lomkhiqizo:

I-Northwind Database ye-Product Table Excerpt
ProductID ProductName IsigabaID IsibaloPerU Intengo yokukodwa
1 Chai 1 Amabhokisi 10 x izikhwama ezingu-20 18.00
2 Chang 1 Amabhodlela angu-24 - 12 oz 19.00
3 Isiraphu esisaziwayo 2 Amabhodlela ama-12 - 550 ml 10.00
4 I-Chef Anton's Cajun Seasoning 2 48 - 6 oz izimbiza 22.00
5 I-Gumbo Mix Mix ye-Chef Anton 2 36 amabhokisi 21.35
6 Ugogo we-Boysenberry Spread 2 12 - 8 oz izimbiza 25.00
7 Amapheya omile omalume ka-Uncle Bob's 7 12 - 1 lb ama-pkgs. 30.00

Ikholomu ye- ProductID yikhiye eliyinhloko letafula. Ikwazisa i-ID eyingqayizivele kumkhiqizo ngamunye.

Le tafula iqukethe ikholomu yekhiye yangaphandle, i- CategoryID . Wonke umkhiqizo wethebula leMkhiqizo uxhuma ekungeneni kumathebula wezinhlaka ezichaza isigaba somkhiqizo.

Qaphela le ngcaphuno kusuka etafuleni lethebula lezinombolo:

I-Northwind Database Ithebula le-Table Excerpt
IsigabaID IsigabaName Incazelo
1 Ukuphuza Iziphuzo ezinomsoco, ama-coffees, amathiya, ubhiya, kanye nama-ales
2 Ama-Condiments Ama-sauces amnandi namnandi, avuselela, asakazeka, futhi ahlaziye
3 Ukuvuma Ama-dessert, ama-candies, nama-sweetbreads
5 Imikhiqizo yobisi Amachizi

I- CategoryID yekholomu yikhiye eyinhloko yekholomu. (Akanayo ukhiye wangaphandle ngoba awunaso isidingo sokufinyelela elinye ithebula.) Wonke ukhiye wangaphandle kwiThebula lomkhiqizo uxhumanisa ukhiye oyinhloko kumathebula wezinhla. Isibonelo, umkhiqizo we-Chai unikezwa isigaba esithi "IziPhuzo", kuyilapho iSiraphu e-Aniseed isesigabeni se-Condiments.

Lolu hlobo lokuxhumanisa ludala izindlela eziningi zokusebenzisa nokusebenzisa kabusha idatha kudatha lokuxhumana.