什么是“= null”和“ IS NULL“ [英] what is "=null" and " IS NULL"

问题描述

= null和IS NULL有什么区别？ c> WHERE 子句中，

code> column = null 永远不会是真的，使用null这种方式是无效的，你需要说列IS NULL 或列IS NOT NULL 。这说明 NULL 的特殊性质，它不是一个检查其相等性的值，它是一个未知的值，因此您需要使用

您可以指定<$ c

$ c> NULL 值使用 = 等于。例如： UPDATE TableX SET Column = NULL ...

链接：

< a href =http://en.wikipedia.org/wiki/Null_%28SQL%29 =noreferrer>维基百科NUll（SQL）

w3schools SQL NULL值

SQL教程，请参阅IS NULL运算符部分

What is the difference between "=null" and "IS NULL"? How are they used differently?

解决方案

In a WHERE clause, column=null will never be true, it is not valid to use null this way, you need to say column IS NULL or column IS NOT NULL. This speaks to the special nature of NULL, it is not a value to check for equality of, it is an unknown value, so you need to use the IS or IS NOT syntax.

You may assign something the NULL value using the = equal. For example: UPDATE TableX SET Column=NULL...

links:
Wikipedia NUll (SQL)
w3schools SQL NULL Values
SQL Tutorial, see IS NULL Operator section

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