SQL NULL Function

Hukumance SQL ISNULL(), NVL(), IFNULL() da COALESCE()

Bai cikakken "Products" tabbin:

P_Id ProductName UnitPrice UnitsInStock UnitsOnOrder
1 computer 699 25 15
2 printer 365 36 　
3 telephone 280 159 57

Bai "UnitsOnOrder" ya'a yi iya da daidai NULL.

A na amma yin a hukumance SELECT:

SELECT ProductName,UnitPrice*(UnitsInStock+UnitsOnOrder)
FROM Products

A cikin wasan gajeren hanyar a kusa, bai daɗaɗɗa ba ne amma kamar yadda "UnitsOnOrder" yana da NULL, kuma yana da NULL.

ISNULL() funtiyawa na Microsoft yana da iyaka kan kada a kawarwace NULL.

NVL(), IFNULL() da COALESCE() funtiyawa kuma za a samu auriyawace da yana da iyaka.

A kusa, a bincike na 0 amma NULL.

A kusa, bai daɗaɗɗa ba ne amma kamar yadda "UnitsOnOrder" yana da NULL, kuma yana da iyaka, kuma ISNULL() yana da 0.

SQL Server / MS Access

SELECT ProductName,UnitPrice*(UnitsInStock+ISNULL(UnitsOnOrder,0))
FROM Products

Oracle

Oracle ba ta da funtiyawa ISNULL(). Kuma, a kawarwace NVL() funtiyawa a ga kada a samu auriyawace da yana da iyaka:

SELECT ProductName,UnitPrice*(UnitsInStock+NVL(UnitsOnOrder,0))
FROM Products

MySQL

MySQL kuma ta da funtiyawa da yana da iyaka ISNULL(). Kuma, yana da iyaka da ISNULL() funtiyawa na Microsoft.

A MySQL, a kawarwace IFNULL() funtiyawa, kamar yadda a ya:

SELECT ProductName,UnitPrice*(UnitsInStock+IFNULL(UnitsOnOrder,0))
FROM Products

atawace a kawarwace COALESCE() funtiyawa, kamar yadda a ya:

SELECT ProductName,UnitPrice*(UnitsInStock+COALESCE(UnitsOnOrder,0))
FROM Products