Question

I have this table on my MySQL server:

id      name    url     type    ut      lastcheck
1       Name1   url1    1       5       2011-06-28 12:21:46
2       Name2   url2    1       10      2011-06-28 12:21:46
3       Name3   url3    1       12      2011-06-28 12:21:46
4       Name4   url4    1       1       2011-06-28 12:21:46

ut means update time, in minutes. I want to develop a script using MySQL commands that retrieves me only the elements that complains this statement:

NOW() – lastcheck=>ut

I’m developing in php and I know how to do this retrieving all the elements and then using simple php operations to filter the elements I need, BUT I don’t want any more load in my script. So I want my MySQL server to do all the work but I have no idea how to build the SQL query to do this.

I know that MYSQL can make difference between dates using SELECT TIMEDIFF(NOW(), '2010-11-26 12:00:00'); for example.

Answer 1

If I have understood correctly, you need to select the rows where the number of minutes since the last check is greater than ut?

You should be able to use the TIMESTAMPDIFF command for that:

SELECT * FROM table WHERE ut < TIMESTAMPDIFF(MINUTE,lastcheck,NOW());

The TIMESTAMPDIFF command allows you to specify the units that you wish to be output so it should give you exactly what you need.