Сложение дат

$row = mysqli_fetch_assoc(mysqli_query($connect, "SLECT `date`, `date_two` FROM `dates`"));
$row['date'];
$row['date_two'];

<?php
$data_1="2016-12-01";
$data_2="2012-11-11";
 
list($year_1, $month_1, $day_1) = explode("-", $data_1);
list($year_2, $month_2, $day_2) = explode("-", $data_2);
$year=$year_1+$year_2;
$month=$month_1+$month_2; 
$day=$day_1+$day_2; 
echo $year,'-'.$month,'-'.$day;
?>

time();

$tomorow = time() + 86400;

date();

$data_1="2016-12-01 12:13:10";
$data_2="2012-11-11" 12:00:00;
 
list($year_1, $month_1, $day_1, $hour_1, $minute_1, $second_1) = explode("-", $data_1);
list($year_2, $month_2, $day_2, $hour_2, $minute_2, $second_2) = explode("-", $data_2);
$year=$year_1+$year_2;
$month=$month_1+$month_2;
$day=$day_1+$day_2;
$hour=$hour_1+$hour_2;
$minute=$minute_1+$minute_2;
$second=$second_1+$second_2;
echo $year,'-'.$month,'-'.$day,' '.$hour,'-'.$minute,'-'.$second;

$data_1="2016-12-01 12:13:10";
$data_2="2012-11-11 11:10:30";
 
$var_1 =  split('[-: ]', $data_1);
$var_2 =  split('[-: ]', $data_2);
 
$year=$var_1[0]+$var_2[0];
$month=$var_1[1]+$var_2[1];
$day=$var_1[2]+$var_2[2];
$hour=$var_1[3]+$var_2[3];
$minute=$var_1[4]+$var_2[4];
$second=$var_1[5]+$var_2[5];
 
echo $year,'-'.$month,'-'.$day,' '.$hour,'-'.$minute,'-'.$second;

strtotime()

$sData_1 = "2016-02-24 8:40:00";
$sData_2 = "1971-01-01 00:00:00"; // Ровно год от 1970-01-01 00:00:00
 
$sDataSec1 = strtotime($sData_1); echo ($sDataSec1.'<br>');
$sDataSec2 = strtotime($sData_2); echo ($sDataSec2.'<br>');
$sDataSec3 = $sDataSec1 + $sDataSec2; echo ($sDataSec3.'<br>');
$sDataSec4 = date ("Y m d H:i:s", $sDataSec3); echo ($sDataSec4.'<br>');

$sData_s = "1970-01-01 00:00:01"; // Секунда
$sData_i = "1970-01-01 00:01:00"; // Минута
$sData_H = "1970-01-01 01:00:00"; // Час
$sData_d = "1970-01-02 00:00:00"; // День
$sData_m = "1970-02-01 00:00:00"; // Месяц
$sData_Y = "1971-01-01 00:00:00"; // Год
 
$sData_s = strtotime($sData_s); echo ($sData_s.' Секунда<br>');
$sData_i = strtotime($sData_i); echo ($sData_i.' Минута<br>');
$sData_H = strtotime($sData_H); echo ($sData_H.' Час<br>');
$sData_d = strtotime($sData_d); echo ($sData_d.' День<br>');
$sData_m = strtotime($sData_m); echo ($sData_m.' Месяц<br>');
$sData_Y = strtotime($sData_Y); echo ($sData_Y.' Год<br>');

$datetime1 = date_create('2012-03-27 ');
$datetime2 = date_create('2012-05-01');
$interval = date_diff($datetime1, $datetime2);
echo $interval->format('%y год(а) %m месяц(ов) %d дней');

<?php
        //Enter your code here, enjoy!
 
$date_1 = new DateTime( "2016-12-01 12:13:10" );
$date_2 = new DateTime( "2012-11-11 12:00:00" );
$date_3 = new DateTime( "2016-00-00 12:00:00" );
 
$intv_tmp = $date_2->diff( $date_1 );
 
$date_result = $date_3->add( $intv_tmp );
 
print_r( $date_result );

<?php
        //Enter your code here, enjoy!
 
function getNewDate( $date1 , $date2 ) {
    $date_1 = new DateTime( $date1 );
    $date_2 = new DateTime( $date2 );
    $intv_tmp = $date_1->diff( $date_2 );     
    if ( $intv_tmp->invert ) {
        $date_1->sub( $intv_tmp );
        return $date_1;
    }
    $date_2->add( $intv_tmp );
    return $date_2;
}
 
$newDate = getNewDate( "2016-12-01 12:13:10" , "2017-11-11 12:00:00" );
 
 
print_r( $newDate );

<?php
        //Enter your code here, enjoy!
 
function getNewDate( $date1 , $date2 ) {
    $date_1 = new DateTime( $date1 );
    $date_2 = new DateTime( $date2 );
    $intv_tmp = $date_1->diff( $date_2 );     
    if ( $intv_tmp->invert ) {
        $date_1->sub( $intv_tmp );
        return $date_1->format('Y-m-d H:i:s');
    }
    $date_2->add( $intv_tmp );
    return $date_2->format('Y-m-d H:i:s');
}
 
echo getNewDate( "2016-12-01 12:13:10" , "2017-11-11 12:00:00" );

<?php
        //Enter your code here, enjoy!
 
function getNewDate( $date1 , $date2 ) {
    $date_1 = new DateTime( $date1 );
    $date_2 = new DateTime( $date2 );
    $intv_tmp = $date_1->diff( $date_2 );     
    
    return $intv_tmp->format('%Y-%m-%d %H:%i:%s');
}
 
echo getNewDate( "2016-12-01 12:13:10" , "2017-11-11 12:00:00" );