Comparing dates via > and < operators

All across my php code i'm storing dates and times in UTC, but i'm also using mysql to store datetimes (also in utc).

is there any way that date compariso开发者_如何学JAVAns can fail with the greater than and less than operator?

        $curdate=date('Y-m-d H:i:s');
        if($start_datetime>$curdate)

Nope.
There is no way for them to fail.
Mysql date format is intentionally made for this purpose.

There is not a single reason to convert it in whatever else format to compare.

PHP: change date into UNIX timestamp using strtotime() and then u can compare.

MySQL:

change dataType of date column to DateTime and then u can compare below way:

$d1 = new DateTime('2008-08-03 14:52:10');
$d2 = new DateTime('2008-01-03 11:11:10');

var_dump($d1 == $d2);
var_dump($d1 > $d2);
var_dump($d1 < $d2);

A direct datetime compare won't fail. You can do that.

A timestamp comparison would be faster, but I don't think such a micro-improvement in performance would be something to look for in a php application, plus you'll have to take into account the 2030 bug.

I prefer to compare the 'Seconds since the Unix Epoch (January 1 1970 00:00:00 GMT)'. Of course, this is only good for dates on/after 1970.

Given that $date1 and $date2 are two date variables to compare:

if (date("U",$date1) > date("U",$date2)) {
  // $date1 is more recent than $date2
} else {
  // $date1 is older than (or equal to) $date2
}

strtotime($curdate) < strtotime($start_datetime)

strtotime() returns a int rperesenting the Seconds that passed since 01.01.1970 That means if $curdate date is "2011-01-01 12:00:00" and $start-datetime is "2011-01-01 12:00:01" then $start-datetime is bigger then $curdate because strtotime returns an integer for $start-datetime that is exactly one bigger than $curdate.