两个时间戳之间无法区分

Question

I want return the number of dates which have a difference less than 30 minutes. These are the records stored in the database:

id | last_login
0    2019-02-11 17:22:47
1    0000-00-00 00:00:00
2    2019-02-11 17:22:03
3    0000-00-00 00:00:00
4    0000-00-00 00:00:00

the result of the query should be 2, but I get 1:

$time = strtotime('+30 minutes');

return $this->db->select('COUNT(last_login) AS users_online')
    ->from('login')
    ->where('UNIX_TIMESTAMP(last_login) < ' . $time)
    ->get()->num_rows();

Answer 1

There are two problems with your code here. The first, is you are cutting everything down to 1 record with an implicit group thanks to count() - and then getting the number of records returned via num_rows().

The second issue is you are getting every single record in the table where the last login is less than 30 minutes in the future... Which will always be every row.

echo date('H:i') . "
" . date('H:i', strtotime('+30 minutes'));

Yields:

16:38
17:08