Question

I am going through an older php application with some functional issues. I came across the following code that appears to be designed to reset the ids in a table:

    SET @num := 0;
    UPDATE `pop_table` SET id = @num := (@num+1);
    ALTER TABLE `pop_table` AUTO_INCREMENT =1;

So… what in the world is an ‘:=’ operator for?? – and what would be the alternative in this particular snippet?

I’ve searched here, php.net, google, apparently “:=” is either to small or too obscure to find, or I just don’t know how to commit a proper search for it. Thanks for any thoughts.

Answer 1

This is not PHP Code. It’s MySQL.

This is a MySQL Function with

SET @num := 0

which means that the value 0 is assigned to the variable @num (refer to the MySQL Manual)

This is used in

UPDATE pop_table SET id = @num := (@num+1);

To make it more understandable, the PHP equivalent would be:

$num = 0; (this is not really comparable, just to get the idea)

UPDATE

I was inspired by the comments to do the NOT RECOMMENDED PHP solution.

$query = mysql_query("SELECT id FROM pop_table ORDER BY id ASC");
$id = 0;
while($result = $mysql_fetch_assoc($query)) {
    $id++
    mysql_query("UPDATE pop_table SET id = " . $id . " WHERE id=" . $result["id"]);
}
mysql_query("ALTER TABLE `pop_table` AUTO_INCREMENT =1;");

didn’t test it, but should work.