Sql 执行空值记录

我正在尝试执行表

newtimeattention

…

TotalTime

数据类型

nchar（10）

……没什么

select * from newtimeattendance where TotalTime =  'null'

select * from newtimeattendance where TotalTime =  'Null'

select * from newtimeattendance where TotalTime =  null

select * from newtimeattendance where TotalTime =  Null

select * from newtimeattendance where TotalTime =  NULL

……没什么

select * from newtimeattendance where TotalTime =  'null'

select * from newtimeattendance where TotalTime =  'Null'

select * from newtimeattendance where TotalTime =  null

select * from newtimeattendance where TotalTime =  Null

select * from newtimeattendance where TotalTime =  NULL

……没什么

select * from newtimeattendance where TotalTime =  'null'

select * from newtimeattendance where TotalTime =  'Null'

select * from newtimeattendance where TotalTime =  null

select * from newtimeattendance where TotalTime =  Null

select * from newtimeattendance where TotalTime =  NULL

……没什么

select * from newtimeattendance where TotalTime =  'null'

select * from newtimeattendance where TotalTime =  'Null'

select * from newtimeattendance where TotalTime =  null

select * from newtimeattendance where TotalTime =  Null

select * from newtimeattendance where TotalTime =  NULL

……没什么

select * from newtimeattendance where TotalTime =  'null'

select * from newtimeattendance where TotalTime =  'Null'

select * from newtimeattendance where TotalTime =  null

select * from newtimeattendance where TotalTime =  Null

select * from newtimeattendance where TotalTime =  NULL

……没什么

select * from newtimeattendance where TotalTime =  'null'

select * from newtimeattendance where TotalTime =  'Null'

select * from newtimeattendance where TotalTime =  null

select * from newtimeattendance where TotalTime =  Null

select * from newtimeattendance where TotalTime =  NULL

当我选择整个表时，我可以看到有一些

NULL

TotalTime

值

它很小，为什么不起作用？有没有一种方法（特殊方法）可以用

nchar

type执行“NULL”

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提前感谢

您需要使用

为空

select * from newtimeattendance where TotalTime IS NULL

MySQL文档提供了一些关于处理空值的好信息：

是的。基本SQL；）三元逻辑-与NULL的比较总是失败的，因此需要特定的语法。