Comparing timestamp to current time from database

Question

I need to test current time against a datetime from database, if it has been 30 mins then execute code, if not then dont. This is where I am at and I am stuck:

$link = mysqli_connect("hostname", "username", "password", "database");
$q = "SELECT id FROM dwCache ORDER BY id DESC LIMIT 1";
$qu = mysqli_query($link, $q);

while($row=mysqli_fetch_array($qu, MYSQL_ASSOC)){
        $id = $row['id'];
        $cache = $row['cache'];
        $timest = $row['time'];
    }

$newTime = 
$difference = $timest
if($timest >= )

As you can see towards the bottom I lose it as I am not sure what to do.

$timest returns : 2013-02-01 12:36:01 as the format Y-m-d h-i-s

Apologies on double post, other deleted.

Answer 1

SELECT id FROM dwCache ORDER BY id DESC LIMIT 1

you'll get only id field, it's the first. The second, for time converting: MySQL convert datetime to Unix timestamp

Third: you can convert your time string using strtotime function.

Answer 2

I like to use unix timestamps in this situation.

$timest = date('u'); // gets the unix timestamp
$q = "SELECT id 
      FROM `dwCache` 
      WHERE {$timest} - UNIX_TIMESTAMP(`timestamp_col`) > 1800";

Explanation:

This basically calculates the difference between the current time and the time in the table column. If it's higher than 1800 (30 minutes), it will select the row, and your PHP code will be executed.

Advantages

There are some advantages to using this instead of the PHP check you started doing. You will select fewer rows, thus occupy less memory.

PS:

Thumbs up for using MySQLi !

Answer 3

First convert $timest to timestamp

$time = strtotime($timest);

$curtime = time();

if(($curtime-$time) > 1800) {     //1800 seconds
  //do stuff
}

Answer 4

do it all in sql statement

SELECT id FROM `dqCache` WHERE `time`<DATE_SUB(NOW(), INTERVAL 30 MINUTE);

This will return everything from your table where the time column is before 30 minutes before now.