通过MySql命令中的foreach循环加快执行速度

Question

I have a PHP foreach statement, looping through a large number of $icons .

For each icon, the DB-column sequence needs to be updated. As follows:

foreach ($icons as $key => $icon) {
    // MySql pseudo-code:
    UPDATE `tbl_icon2album` 
    SET `sequence`= $key +1 
    WHERE iconID= $icon['id']       
}

My problem : this becomes very slow for a large number of icons.

My question : Can I speed this up by executing one MySql command that would somehow include the foreach loop?

Much obliged...

Answer 1

You could put all your updates in another table, and update using a single query, eg

 UPDATE tbl_icon2album, some_other_table
 SET    sequence = some_other_table.new_key_value
 WHERE  iconID = some_other_table.icon_reference

Answer 2

How many keys are you updating? Is it the iteration that is slow, or are you doing this thousands of times?

You could use the "in" clause.

ie:

 update table set key=key+1 where blah in ('1','2','3');

and you could iterate through the for loop to construct a variable passed to in:

ie:

 $iconlist = "";
 foreach ($icons as $key => $icon) {
   if (!$iconlist) { $iconlist = "($icon" }
   else 
   { $iconlist .= ",$icon" }
 }
 if ($iconlist) { 
   $iconlist .= ")";
   $query = "update table set key=key+1 where icon in $iconlist";

 }

Answer 3

If you use prepared statements then you can prepare the query once, bind the parameters, and then execute within the loop. This could be faster as it is usually preparing the query that takes up time. For example:

$stmt = $mysqli->prepare("

  UPDATE
    `tbl_icon2album`
  SET
    `sequence` = ?
  WHERE
    `iconID` = ?

");

$stmt->bind_param('ii', $sequence, $icon_id);

foreach ($icons as $key => $icon)
{

  $sequence = $key + 1;

  $icon_id = $icon['id'];

  $stmt->execute(); 

}