MySQL add time to column

Question

Bit of a puzzle for you guys. I can come up with blunt workaround (below) but I thought it would present it to you all to see if there was a more elegant solution out there. Keep in mind I'm looking for a PHP or MySql only solution.

Tables is 'candles2'. I have a MySQL TEXT column 'time' that has a datestamp in it ( e.g. 2010.08.13 19:30 ). Please don't ask why it is a TEXT field :). I have a second TEXT column 'timeframe' that lists a denomination of time (e.g. '15m', '30m', '1h', '4h' or 'daily'). 'id' is the primary key.

I want to add the amount of time in 'timeframe' to 'time'.

So for example if 'time' == '2010.08.13 19:30' and 'timeframe'==15m then it would update 'time' with '2010.08.13 19:45' (notice the addition of 15 minutes).

Here is what I was thinking:

//PHP querying the DB:

//using UNIX_TIMESTAMP to make the datetime usable by PHP
$sql = "SELECT UNIX_TIMESTAMP(time), timeframe, id FROM candles2";
$result = mysql_query($sql);

//loop through rows
while($row = mysql_fetch_array($result))
{
 //call function to determine the appropriate # of seconds to add
 $newTime = newTime($row['time'],$row['timeframe']);

 //build UPDATE query and update row
 $update_query = "UPDATE candles2 SET 'time'= FROM_UNIXTIME(" . $newTime . ") WHERE id='".$row['id']."'";
 $update_result = mysql_query($update_query);
}

//PHP Function to add appropriate seconds

function newTime($oldtime,$timeframe)
{
 switch ($timeframe)
  {
        case "15m":  return($oldtime + 15 * 60);
 case "30m":  return($oldtime + 30 * 60);
        case "1h":  return($oldtime + 60 * 60);
 case "4h":  return($oldtime + 240 * 60);
 case "daily":         return($oldtime + 1440 * 60);
 default:         die("whoops, something broke"); 
   }
}

Answer 1

Why not use MySQL's STR_TO_DATE() to transform your text value into a datetime value, then use DATE_ADD() to add the interval? It should be fairly easy to to transform your timeframe into an interval format that MySQL expects (INTERVAL 30 MINUTE for example). You can then use DATE_FORMAT() to get it back into text form.

Answer 2

change your newtime function to the following:

function newTime($oldtime,$timeframe)
{
  $new_time = strtotime( $oldtime );

  switch ($timeframe)
  {
    case "15m":
      $new_time = $new_time + 15 * 60;
      break;

    case "30m":
      $new_time = $new_time + 30 * 60;
      break;

    case "1h":
      $new_time = $new_time + 60 * 60;
      break;

    case "4h":
      $new_time = $new_time + 240 * 60;
      break;

    case "daily":
      $new_time = $new_time + 1440 * 60;
      break;
  }

  return date( 'Y.m.d H:i', $new_time );
}

Answer 3

You can use the PHP DateTime class to make date and time calculations much simpler:

$timeframe = '15m';
$time = '2010.08.13 19:30';

$dt = DateTime::createFromFormat('Y.m.d G:i', $time);
$new_dt = $dt->add(
  new DateInterval('PT' . strtoupper(
    str_replace('daily', '24h', $timeframe))));

echo date_format($new_dt, 'Y.m.d G:i');
// 2010.08.13 19:45

Or, for a purely MySQL solution, you could use a cursor to create a prepared statement to update the rows:

DELIMITER //
DROP PROCEDURE IF EXISTS update_candles//
CREATE PROCEDURE update_candles()
BEGIN
  DECLARE var_id INT;
  DECLARE var_time, var_timeframe TEXT;

  DECLARE var_done INT DEFAULT 0;
  DECLARE csr_candles CURSOR FOR
    SELECT id, time, timeframe FROM candles2;
  DECLARE CONTINUE HANDLER FOR NOT FOUND SET var_done = 1;

  OPEN csr_candles;

  REPEAT
    FETCH csr_candles INTO var_id, var_time, var_timeframe;
    IF NOT var_done THEN
      SET
        @id        := var_id,
        @time      := var_time,
        @timeframe := var_timeframe,
        @unit1     := SUBSTR(@timeframe, -1),
        @unit2     := MAKE_SET(FIND_IN_SET(@unit1, 'm,h,,y'), 'MINUTE', 'HOUR', 'DAY'),
        @interval  := FORMAT(@timeframe, 0) | 1,
        @var_sql   := CONCAT('UPDATE candles2 SET time = TIMESTAMPADD(', @unit2, ',?,?) WHERE id = ?');

      PREPARE sql_stmt FROM @var_sql;
      EXECUTE sql_stmt USING @interval, @time, @id;
    END IF;
  UNTIL var_done END REPEAT;

  DEALLOCATE PREPARE sql_stmt;
END;
//
DELIMITER ;

CALL update_candles;