Need help with multiple WHERE clause

I have an UPDATE query I'开发者_运维技巧d like to perform.

But there need to be 2 conditions met before we can update a quantity in the database.

First, the sessions_id() must match one of the sessionid's in the sessionid column, and second, the Description of the product must match the description of the product corresponding to the sessionid.

Here's what I have:

mysql_query(UPDATE cart 
               SET quantity = $q, 
             WHERE sessionid = "'.session_id().'" 
               AND description = $d') or die(mysql_error());

Now, it is giving me the following error:

You have an error in your SQL syntax;

check the manual that corresponds to your MySQL server version for the right syntax to use near 'WHERE sessionid="bqlbh5rdogbhmq70skhtkbvmb0" AND description=$d' at line 1

However, I have copied this update query straight from W3Schools, so it must be correct, right? Any help at all would be appreciated.

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The error occurs because of the ',' sign before the WHERE statement. The correct query would be:

mysql_query( "UPDATE cart SET quantity = " . $q . " WHERE sessionid = "' . session_id( ) . '" AND description = " . $d . "" ) or die( mysql_error( ) );

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remove the , (comma) after $q

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the code you have pasted is badly formatted, and i doubt the code used in your app.

$sql = sprintf(
    "UPDATE `cart` SET `quantity` = '%d' WHERE `sessionid` = '%s' AND `description` = '%s'", 
    $q, 
    session_id(), 
    $d
);
mysql_query($sql);

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It should look that way:

mysql_query("UPDATE cart SET quantity = $q WHERE sessionid='" .session_id(). "' AND description = '$d'") or die(mysql_error());

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Also you have problem with the single quotes here .'" AND description=$d') and $d is not parsed. This will result wrong SQL query. Change the single quotes to double quotes or just use string append . to append the value of $d, not the literal $d

example :

$a = 5;
$b = 'a is $a'; // a is $a;
$c = "a is $a"; // a is 5