Php mysql, variable help query help

I have this mysql query:

UPDATE `table`.`wp_12_postmeta` 
   SET `meta_value` = 'yyy' 
 WHER开发者_Go百科E `wp_12_postmeta`.`meta_id` =5 
 LIMIT 1 ;

How do i incorporate this:

• instead of wp_12_ i want a variable $prefix (variable holds wp_4_, wp_3_, etc)
• instead of yyy i want a value $perf (variable is a name )
• instead of 5 i want a value $meta_id (variable is a nr)

Thank u!

P.S.

here is what i use and it works:

$wpdb->query("UPDATE ".$prefix."postmeta SET meta_value = '".$perf."' WHERE meta_id = '".$meta_id."' LIMIT 1 "); 

Problem is, when i execute this query, severl post meta fields are updated, instead of just one. Ty

Use:

$query = sprintf("UPDATE `table`.`%s` 
                    SET `meta_value` = '%s' 
                  WHERE `%s`.`meta_id` = %d 
                   LIMIT 1 ",
                 mysql_real_escape_string($prefix),
                 mysql_real_escape_string($perf),
                 mysql_real_escape_string($prefix),
                 mysql_real_escape_string($meta_id));

Here's how I would write this with PDO:

$prefix = "wp_4_";
$sql = "UPDATE `table`.`{$prefix}postmeta` SET `meta_value` = ? 
  WHERE `{$prefix}postmeta`.`meta_id` = ? LIMIT 1";

$stmt = $pdo->prepare($sql);
$stmt->execute(array($perf, $meta_id));