PHP自动更改日期+1天

I am writing a email application which has a graphical statistic page, The graph shows how many e-mails a user has send per day, I can get the data for the graph correctly for each day only if I hard code it, but I would like to know how to make a automatic mechanism to.

this is a query I use to get data from database:

Query:

 $today = "SELECT COUNT(tbl_template_log.user_id) FROM tbl_template_log ";
            $today .= "WHERE tbl_template_log.user_id='$id'";
            //$today .= " AND tbl_template_log.send_date > '2014-05-21' ";
            //$today .= "AND tbl_template_log.send_date < '2014-05-21'";

But I would like to have variables instead of the dates like $start and $finish that are readjusted for everyday day, So user can se an actual daily data without me manually changing the data....?

my PHP class:

class statsToday{

function con()
{
    require_once('connect.php');
    $DB = new dbConnect();
    return $DB->connect();
    }

    public $start;
    public $finish;

    public function getStats($user){

            $user = "SELECT user_id FROM tbl_user WHERE ott_email='$user'";
            $query = mysqli_query($this->con(), $user);
            $count = mysqli_num_rows($query);

            if($count == 1){

             while($row = mysqli_fetch_assoc($query)){
                 $id = $row['user_id'];
             }

            $today = "SELECT COUNT(tbl_template_log.user_id) FROM tbl_template_log ";
            $today .= "WHERE tbl_template_log.user_id='$id'";
            //$today .= " AND tbl_template_log.send_date > '$start' ";
            //$today .= "AND tbl_template_log.send_date < '$finihs''";
            $query_today = mysqli_query($this->con(), $today);
            $today = mysqli_fetch_row($query_today);

            echo $today[0];
        }

    }
}

Could somebody suggest a solution..?

If you only want "today" you can use the built in mysql date function in the form of:

$today = "SELECT COUNT(tbl_template_log.user_id) FROM tbl_template_log ";
$today .= "WHERE tbl_template_log.user_id='$id'";
$today .= " AND DATE(send_date) = DATE(NOW())";

Or to do all in the last week:

$today = "SELECT COUNT(tbl_template_log.user_id) FROM tbl_template_log ";
$today .= "WHERE tbl_template_log.user_id='$id'";
$today .= " AND tbl_template_log.send_date >= '" . date('Y-m-d', strtotime('-1 week')) . "' ";
$today .= "AND tbl_template_log.send_date =< '" . date('Y-m-d', strtotime('today')) . "'";

Another way, a little easier to use if you are indexing the database on the send_date field:

$today = "SELECT COUNT(*) 
  FROM tbl_template_log
  WHERE user_id='$id'
  AND send_date BETWEEN CURDATE() AND CURDATE() + INTERVAL 1 DAY";