“"和"= null"和“是"NULL"吗? [英] What's the difference between " = null" and " IS NULL"?

问题描述

"= null"和"IS NULL"之间有什么区别?它们的用法有何不同?

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

推荐答案

在WHERE子句中，column=null永远不会为true，以这种方式使用null无效，您需要说column IS NULL或column IS NOT NULL.这说明了NULL的特殊性质，它不是要检查其是否相等的值，它是未知值，因此您需要使用IS或IS NOT语法.

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.

您可以使用=等于来分配NULL值.例如:UPDATE TableX SET Column=NULL...

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

链接:
维基百科NUll(SQL)
w3schools SQL NULL值
SQL教程，请参见"IS NULL运算符"部分

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

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