使用MySQL检查空字段 [英] Checking for an empty field with MySQL

问题描述

我写了一个查询来检查是否符合某些条件的用户，一个是他们有电子邮件地址.

I've wrote a query to check for users with certain criteria, one being they have an email address.

我们的网站将允许用户拥有或没有电子邮件地址.

Our site will allow a user to have or not have an email address.

$aUsers=$this->readToArray('
 SELECT `userID` 
 FROM `users` 
 WHERE `userID` 
 IN(SELECT `userID`
         FROM `users_indvSettings`
  WHERE `indvSettingID`=5 AND `optionID`='.$time.')
  AND `email`!=""
 ');

这是检查SQL中的空字段的最佳方法吗?我刚刚尝试过"IS NOT NULL"，但仍然返回用户记录，而他们没有电子邮件地址.

Is this the best way to check for an empty field in SQL? I've just tried "IS NOT NULL" and this still returned a users record without them having an email address.

以上查询有效，但出于好奇，我想知道自己是否以正确的方式进行操作.

The query above works but out of curiosity I wondered if I'm doing it the correct way.

推荐答案

空字段可以是空字符串或NULL.

An empty field can be either an empty string or a NULL.

要处理这两种情况，请使用:

To handle both, use:

email > ''

如果表中有很多空电子邮件记录(两种类型)，则可以从range访问中受益.

which can benefit from the range access if you have lots of empty email record (both types) in your table.

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