Training, Open Source computer languages
PerlPHPPythonMySQLApache / TomcatTclRubyJavaC and C++LinuxCSS 
Search for:
Home Accessibility Courses Diary The Mouth Forum Resources Site Map About Us Contact
For 2023 (and 2024 ...) - we are now fully retired from IT training.
We have made many, many friends over 25 years of teaching about Python, Tcl, Perl, PHP, Lua, Java, C and C++ - and MySQL, Linux and Solaris/SunOS too. Our training notes are now very much out of date, but due to upward compatability most of our examples remain operational and even relevant ad you are welcome to make us if them "as seen" and at your own risk.

Lisa and I (Graham) now live in what was our training centre in Melksham - happy to meet with former delegates here - but do check ahead before coming round. We are far from inactive - rather, enjoying the times that we are retired but still healthy enough in mind and body to be active!

I am also active in many other area and still look after a lot of web sites - you can find an index ((here))
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  

This page is a thread posted to the opentalk forum at and archived here for reference. To jump to the archive index please follow this link.

You can Add a comment or ranking to this page

© WELL HOUSE CONSULTANTS LTD., 2024: Well House Manor • 48 Spa Road • Melksham, Wiltshire • United Kingdom • SN12 7NY
PH: 01144 1225 708225 • FAX: 01144 1225 793803 • EMAIL: • WEB: • SKYPE: wellho