Checking for an empty field with MySQL

php sql mysql null
user275074 picture user275074 · Feb 24, 2010 · Viewed 173.1k times · Source

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

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`!=""
 ');

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.

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

Answer

Quassnoi picture Quassnoi · Feb 24, 2010

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

To handle both, use:

email > ''

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

Related questions

How can I prevent SQL injection in PHP?

If user input is inserted without modification into an SQL query, then the application becomes vulnerable to SQL injection, like in the following example: $unsafe_variable = $_POST['user_input']; mysql_query("INSERT INTO `table` (`column`) VALUES ('$unsafe_variable')"); That's …

Read More
MySQL query String contains

I've been trying to figure out how I can make a query with MySQL that checks if the value (string $haystack ) in a certain column contains certain data (string $needle), like this: mysql_query(" SELECT * FROM `table` WHERE `column`.contains(…

Read More
How to 'insert if not exists' in MySQL?

I started by googling, and found this article which talks about mutex tables. I have a table with ~14 million records. If I want to add more data in the same format, is there a way to ensure the record I …

Read More