=和IS mysql之间的区别
因此,我目前在一个具有交互式MySQL Shell提示符的站点上.
So I am on a site at the moment where it has an interactive MySQL Shell prompt.
我一直在寻找一个朋友问的问题,即为什么当我使用关键字IS
时查询失败,但是当我使用=
符号时却有效?"
I was looking up a question that a friend asked which is "why does the query fail when I use the keyword IS
but it works when I use the =
symbol?"
所以我进行了测试,并确定它确实失败了.
So I tested it out and sure enough it does fail.
SELECT name, continent, population FROM world WHERE continent IS 'Asia'
失败,但SELECT name, continent, population FROM world WHERE continent = 'Asia'
正常.
我尝试使用Google搜索来寻找答案,但无济于事.
I have tried googling for an answer but no avail.
任何帮助都会很棒!
IS 对布尔值(不为True/False/NULL)进行测试,其中
IS tests against a boolean(True/False/NULL neither) where as = tests equivalency
IS只能用于返回true,false或NULL的变量.
IS can only be used against variables that return true, false or NULL .