SQL选择查询w / Null参数

Question

我在2个类似的SQL Select Querys'上有错误，我的假设是我错误地使用了NULL。有人看了看，告诉我哪里出错了。

string CountHolidayQuery = "SELECT StartDate, EndDate FROM [Holiday] WHERE PayrollNo = @PayrollNo AND Authorised IS NOT Null";

和

string CountRequestedQuery = "SELECT StartDate, EndDate FROM [Holiday] WHERE PayrollNo = @PayrollNo AND Authorised IS Null";

Answer 1

Authorised = Null无效，应为Authorised IS Null或Authorised IS NOT Null

Answer 2

在SQL中，Null并不像值那样对待，实际上是一种特殊情况，其语法为Is Null和Is Not Null，例如

string CountHolidayQuery = "SELECT StartDate, EndDate FROM [Holiday] WHERE PayrollNo = @PayrollNo AND Autorised Is Not Null";

以及

string CountRequestedQuery = "SELECT StartDate, EndDate FROM [Holiday] WHERE PayrollNo = @PayrollNo AND Authorised Is Null";

在第一个声明中，Authorised不应该为空，它输入错误，而是读取Autorised

Answer 3

应该是＆＃34; IS NOT null＆＃34;，缺少查询IS

SELECT StartDate, EndDate FROM [Holiday] WHERE PayrollNo = @PayrollNo AND Autorised IS NOT Null";

第二个查询Authorised = Null不是有效的sql语法。

Answer 4

我认为您错过了关键字

所以声明如下：

string CountHolidayQuery = "SELECT StartDate, EndDate FROM [Holiday] WHERE PayrollNo = @PayrollNo AND Autorised is NOT Null";