Select a text field from mysql in php - php

Question

usersim interested how do i select a text field form my mysql database, i have a table named users with a text field called "profile_fields" where addition user info is stored. How do i access it in php and make delete it? I want to delete unvalidate people.
PHP code
<?php
//Working connection made before assigned as $connection
$time = time();
$query_unactive_users = "DELETE FROM needed WHERE profile_fields['valid_until'] < $time"; //deletes user if the current time value is higher then the expiring date to validate
mysqli_query($connection , $query_unactive_users);
mysqli_close($connection);
?>
In phpmyadmin the field shows (choosen from a random user row):
a:1:{s:11:"valid_until";i:1370695666;}
Is " ... WHERE profile_fields['valid_until'] ..." the correct way?

Answer 1

Anyway, here's a very fragile solution using your knowledge of the string structure and a bit of SUBSTRING madness:
DELETE FROM needed WHERE SUBSTRING(
profile_fields,
LOCATE('"valid_until";i:', profile_fields) + 16,
LOCATE(';}', profile_fields) - LOCATE('"valid_until";i:', profile_fields) - 16
) < UNIX_TIMESTAMP();
But notice that if you add another "virtual field" after 'valid_until', that will break...

Answer 2

You can't do it in a SQL command in a simple and clean way. However, the string 'a:1:{s:11:"valid_until";i:1370695666;}' is simply a serialized PHP array.
Do this test:
print_r(unserialize('a:1:{s:11:"valid_until";i:1370695666;}'));
The output will be:
Array ( [valid_until] => 1370695666 )
So, if you do the following, you can retrieve your valid_until value:
$arrayProfileData = unserialize('a:1:{s:11:"valid_until";i:1370695666;}');
$validUntil = arrayProfileData['valid_until'];
So, a solution would be to select ALL items in the table, do a foreach loop, unserialize each "profile_fields" field as above, check the timestamp, and store the primary key of each registry to be deleted, in a separate array. At the end of the loop, do a single DELETE operation on all primary keys you stored in the loop. To do that, use implode(',', $arrayPKs).
It's not a very direct route, and depending on the number of registers, it may not be slow, but it's reliable.
Consider rixo's comment: if you can, put the "valid_until" in a separate column. Serializing data can be good for storage of non-regular data, but never use it to store data which you may need to apply SQL filters later.