php+web,提示strtotime有错,显示的是今天的时间,求解答
<input type="text" name="query_start_time" value="<?php if ($query_start_time == '') {
$yesterday =date('Y-m-d 21:00:00', strtotime("-1 day") );
echo $yesterday;
} else {
echo $query_start_time;
} ?>" id="query_start_time">