Abin da ya kamata ka sani game da lambobin NULL

Yi la'akari da Amfani da NULLs don guji Matsalar Matsala

Sabbin masu amfani a duniya na bayanan bayanai suna rikita batun ta musamman ta musamman ga filin - NULL darajar. Wannan darajar za a iya samuwa a cikin wani filin da ke dauke da kowane nau'in bayanai kuma yana da mahimmanci ma'anar a cikin mahallin dangantaka. Zai yiwu mafi kyau mu fara tattaunawa game da NULL tare da wasu kalmomi game da abin da NULL ba :

Maimakon haka, NULL ita ce darajar da ake amfani dashi don wakiltar wani bayanan da aka sani ba. Sau da yawa, masu shirye-shiryen bayanai na bayanai zasuyi amfani da kalmar "darajar NULL", amma wannan ba daidai ba ne. Ka tuna cewa: NULL wani nau'i ne wanda ba'a sani ba inda filin ya bayyana baƙaƙe.

NULL a cikin Ƙarshen Duniya

Bari mu dubi wani misali mai sauƙi: tebur da ke dauke da kaya don 'ya'yan itace. Yi la'akari da cewa kundin mu yana dauke da apples 10 da alamu guda uku. Har ila yau, muna da cin hanci, amma bayanan kundinmu bai cika ba kuma ba mu san yawancin (idan wani) plums suna cikin jari. Yin amfani da NULL darajar, za mu sami lissafin kaya da aka nuna a teburin da ke ƙasa.

Binciken Tsarin Abincin

InventoryID Item Yawan
1 Apples 10
2 Oranges 3
3 Kayan dabbobi NULL


Ba shakka ba daidai ba ne a hada da yawancin 0 don rikodin labaran, domin wannan yana nufin cewa ba mu da wata dabba a cikin kaya. A akasin wannan, muna iya samun wasu nau'i, amma ba mu tabbata ba.

To NULL ko BA NULL?

Za'a iya tsara tebur don yin izinin NULL ko a'a ba.

A nan ne misalin SQL da ke ƙirƙirar tebur na Inventory da ke bada wasu NULLs:

SQL> Sanya GASKIYA TABI (InventoryID INT BA NULL, Sashe na VARCHAR (20) BA NULL, Yawan INT);

Lambar Inventory a nan ba ta yarda da darajar NULL ga InventoryID da ginshiƙan Matakan ba, amma ya ba su izini don Ƙarin Hadin .

Duk da yake kyale darajar NULL daidai ne, NULL dabi'u zai iya haifar da matsala saboda duk kwatancin dabi'u wanda wanda ke cikin NULL yana haifar da NULL kullum.

Don bincika idan kwamfutarka ta ƙunshi dabi'u NULL, yi amfani da IS NULL ko mai kula da IS NOT NULL. Ga misalin IS NULL:

SQL> SANTA DA SANTAWA, DA KUMA, DA KARANTA DAGA GASKIYA YA BAYA BAYA BAYA BAYA BAYA BAYA;

Bamu misalin nan, wannan zai dawo:

InventoryID Item Yawan
3 Kayan dabbobi

Yin aiki akan NULLs

Yin aiki tare da dabi'u na NULL yakan haifar da sakamakon NULL, dangane da aikin SQL . Alal misali, ɗauka cewa A shine NULL:

Mahimman bayanai

Kamfanonin Ƙari

Wadannan su ne kawai wasu misalai na masu aiki da zasu dawo NULL duk lokacin da aiki daya ne NULL. Yawancin tambayoyin da suke da rikice-rikice sun kasance, kuma duk suna da rikitarwa ta dabi'un NULL. Matsayi a gida shi ne cewa, idan ka yarda da dabi'un NULL a cikin bayananka, fahimtar abubuwan da ke faruwa kuma shirya musu.

Wannan shi ne NULL a cikin komi!