decrease values in database from form

[Hellz]

hi,

I want to update a selected fields in a database, the information i want to update comes from a form but i want it to decrease the value. What i mean is:

The user inputs how many of a product they want and i want the stock field in the database to decrease by that many, any help?

 

This is the current code im using but it increase the value not decrease.

 

PHP Code:

$quantity = $_POST['quantity'];
  $sql = "Update item (Stock) VALUES ('$quantity')";
  $result = mysql_query($sql) or die ( mysql_error() );?> 

[kickstart]

Hi

 

Assuming you want to update one row, the table is Item and the unique key is ItemId, and that you have validated the quantity already.

 

$sql = "Update item SET Stock = STOCK - $quantity WHERE ItemId = $ItemId";

 

All the best

 

Keith

[Hellz]

I get this 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 ProductId =' at line 1

 

$quantity = $_POST['quantity'];
	$sql = "Update item SET Stock = STOCK - $quantity WHERE ProductId = $ProductId ";
	$result = mysql_query($sql) or die ( mysql_error() );?> 

 

thats the code im using. ProductId is the key field in the database table. is that right?

 

[kickstart]

Hi

 

Looks right, assuming you have assigned a valid numeric value to $ProductId, that the ProductId column is a numeric field and that $quantity is a valid numeric value.

 

All the best

 

Keith

[Hellz]

yes there both numbers ? just keep gettin the same error

[kickstart]

Hi

 

Echo out $sql just before you execute the query. Lets see what it says there.

 

All the best

 

Keith

[fenway]

Also, if you're not using transactions, you statement isn't thread safe.