How do I update multiple records in a table with a single MySQL query?

Question

Hello. I would like to update multiple records in a MySQL table using a single query. Basically, this is a tasks table, which has assignments for different people on different dates. When these assignments are changed and submitted via the Online form there is a lot of POST data that gets submitted (pretty much all the pending assignments). I've written an algorithm that sorts through all this information and gets what I want out of it, but I'm stuck on writing the query to update the MySQL table:

  // Find the modified records and save their information
  $update = 0;
  for ( $n = 0; $n < $total_records; $n++ )
  {
     if ( $_POST['update'.$n] == true )
     {
        $updates_arr[$update] = array( intval($_POST['user_id'.$n]), intval($_POST['task'.$n]), $_POST['date'.$n] );
        $update++;
     }
  }

  if ( $mysql_db = OpenDatabase() )
  {
     $query  = "UPDATE tasks_tbl";
     if ( $updates_arr[0] )
     {
        $query .= "   SET task = ".$updates_arr[0][1]." WHERE user_id = ".$updates_arr[0][0]." AND date = ".$updates_arr[0][2];
     }

     for ( $n = 1; $n < $updates; $n++ )
     {
        $query .= ",   SET task = ".$updates_arr[$n][1]." WHERE user_id = ".$updates_arr[$n][0]." AND date = ".$updates_arr[$n][2];
     }

     $result = mysql_query( $query, $mysql_db );

     if ( $result )
     {
        $page .= "<p>Success!</p>\n\n";
     }
     else
     {
        $page .= "<p>Error: ".mysql_error()."</p>\n\n";
     }
  }

This is the query that is generated:

UPDATE tasks_tbl 
   SET task = 1 
 WHERE user_id = 16 
   AND date = 2010-05-05,  
   SET task = 1 
 WHERE user_id = 17 
   AND date = 2222-02-22

Any suggestions would be appreciated. Thanks.

Answer 1

I don't think this is possible with one statement. You will need to create separate UPDATE statements:

UPDATE tasks_tbl SET task = 1 WHERE user_id = 16 AND date = 2010-05-05;
UPDATE tasks_tbl SET task = 1 WHERE user_id = 17 AND date = 2222-02-22

You can pass them into mysql_query() as one string separated by ';' if you set mysql to accept multiple queries:

Multiple queries seem to be supported. You just have to pass flag 65536 as mysql_connect's 5 parameter (client_flags)

Answer 2

You can generate a query like this:

UPDATE tasks_tbl SET task=1 WHERE 
    (user_id=16 AND date='2010-05-05') OR
    (user_id=17 AND date='2010-02-22')

There are hacks to avoid using (... and ...) or (... and ...) constructs (concatenate fields and params: "concat(user_id, date) = '". $user_id. $date. "'", but they work a bit slower.

The PHP code:

for ($i = 0; !empty($_POST['update'. $i]; $i++)
    if (intval($_POST['task'.$i]) == 1)
        $cond[] = '(user_id='. intval($_POST['user_id'. $i]).
        ' and date=\''. mysql_real_escape_string($_POST['date'.$i]). '\')';

$query = 'UPDATE tasks_tbl SET task=1 WHERE '. implode(' OR ', $cond). ')';

Edit: I don't quite understand why you need to do that in a single query. How many values task can have? 1, 2, 3, or many more? With 3 values, you can use nested IF(...) functions:

UPDATE tasks_tbl SET task=if('. <imploded tasks with value 1>. ', 1, if('.
<tasks with value 2>. ', 2, if('. <tasks with 3>. ', 3,
task))) /* leave as is otherwise */

Or you may put a simple loop on the code I've given:

for ($j = 1; $j <= 3; $j++)
    for ($i = 0; !empty($_POST['update'. $i]; $i++)
        if (intval($_POST['task'.$i]) == 1)
            $cond[] = '(user_id='. intval($_POST['user_id'. $i]).
            ' and date=\''. mysql_real_escape_string($_POST['date'.$i]). '\')';

    mysql_query('UPDATE tasks_tbl SET task=1 WHERE '. implode(' OR ', $cond). ')');

Answer 3

Are you looking for this:

UPDATE tasks_tbl 
   SET task = 1 
 WHERE (user_id = 16 AND date = 2010-05-05) 
       OR (user_id = 17 AND date = 2222-02-22)

Or you are trying to set 'task' to different values in different rows with a single statement? The latter is just not possible

Answer 4

I would prefer to use a prepared query and loop over the data (inside a transaction if needed). That makes it simpler to understand, which is better for maintainability.

Your code smells of sql injection insecurity, too, which prepared queries would eliminate.

See: http://www.php.net/manual/en/mysqli.prepare.php or even better with PDO prepare:

Answer 5

I disagree with your architecture here, but the following should work. Use at your own risk:

UPDATE
     Tasks_Table
SET
     task =
          CASE
               WHEN user_id = 16 AND date = 2010-05-05 THEN 1
               WHEN user_id = 17 AND date = 2222-02-22 THEN 1
               ...
          END
WHERE
     (user_id = 16 AND date = 2010-05-05) OR
     (user_id = 17 AND date = 2222-02-22) OR
     ...

In your example you have task = 1 in all cases, but with the CASE statement you can change them to be what you need for each case. I'll leave the string building to you.

Answer 6

Thanks for the suggestions, everyone. I ended up going with the multiple queries, as it apparently was not going to be as simple to do, as I had hoped.

    foreach ( $updates_arr as $record => $data ):
       $query  = "UPDATE tasks_tbl";
       $query .= "   SET task = ".$data[1];
       $query .= "   WHERE task_id = ".$data[0];
       $result = mysql_query( $query, $mysql_db );
       if ( !$result )
       {
          break;
       }
       endforeach;