Question

我在SQL Server 2014中进行了简单的选择

SELECT COUNT(*)
FROM SignOffOperations_View 
WHERE Company = 'ASUS' AND Submission_Id = 10 AND IsOperationPerformed <> 1

如果不包含在where子句中，可以选择表中的数据：IsOperationPerformed

Id      Submission_Id Company IsOperationPerformed 
12008   10            ASUS    NULL
2527    10            ASUS    NULL

因此，此查询的结果为0.我不明白为什么。

Answer 1

A value of NULL indicates that the value is unknown. A value of NULL is different 
from an empty or zero value. No two null values are equal. Comparisons between 
two null values, or between a NULL and any other value, return unknown because the 
value of each NULL is unknown.

Null values generally indicate data that is unknown, not applicable, or that the data 
will be added later. For example, a customer's middle initial may not be known at the 
 time the customer places an order.[Source-msdn]

使用查询

SELECT COUNT(*)
FROM SignOffOperations_View 
WHERE Company = 'ASUS' AND Submission_Id = 10 
AND IsOperationPerformed IS NOT NULL
AND IsOperationPerformed <> 1

OR

SELECT COUNT(*)
FROM SignOffOperations_View 
WHERE Company = 'ASUS' AND Submission_Id = 10 AND ISNULL(IsOperationPerformed,-1) <> 1

Answer 2

SELECT COUNT(*)[Total Count]
FROM SignOffOperations_View 
WHERE Company = 'ASUS' AND Submission_Id = 10 
AND IsOperationPerformed IS NOT NULL
AND ISNULL(IsOperationPerformed,0) <> 1

如果值为False且为Bad，则SQL Query工作正常 - 如果为Null

2 个答案: