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php sql problem

Posted by phillipmulvaney (phillipmulvaney), 29 April 2004
I am having trouble with some simple maths here.
I want to retrieve "quantity" from table "a" subtract 1 from the "quantity" and then post this new "quantity" back to the database.
I can retrieve the "quantity" but when I subtract 1 from it nothing happens.

Here is the code:

$table_name = "a";

$sql = "SELECT quantity FROM $table_name
       WHERE barcode = '$_POST[barcode]'";

$result = @mysql_query($sql,$connection)
         or die(mysql_error());

$num = mysql_num_rows($result);
$sum = 0;

// want to take 1 from quantity
$sum = quantity --;
quantity = $sum;

//now want to post the new quantity
// back to the database
$sql = "update a set quantity
       where barcode = '$_POST[barcode]'";


Posted by admin (Graham Ellis), 29 April 2004
Answer linked (somewhat) to your other post.

You've carefully written an sql command into the $sql variable, but you haven't run mysql_query on the variable to send it across to the MySQL daemon  

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