PHP and SQL maths

Question

This part of PHP and SQL is totally new to me where I need to use maths to update a table.

I currently have a table avis_credits with one row only in this table

The table deducts credits as the user uses the system from qty_credits, but i want to be able to add additional credits to his account as per example:

Client has currently 10 credits left he purchases 100 credits so the system must take the current credits and add the 100 to it giving me the 110 credits. I am doing this currently manual adding it my side and updating the table with this expresion.

 "UPDATE avis_credits SET credits='$qty_credit'";

What I would like is that the system looks up the current credits and adds the new credits to the row.

I have tried this

 "UPDATE avis_credits SET credits='<?php echo qty_credit?> + $qty_credit'";

But it is not working at all. Is it because I am trying to do too many functions in the one string? Or is it because The maths equation is wrong as I have no idea how to write it?

Prix · Accepted Answer · 2013-08-28 09:26:39Z

2

On your first query you're not doing any math you are purely changing it to the value of your variable:

"UPDATE avis_credits SET credits='$qty_credit'";

So credits becomes the value of $qty_credit.

On your second query <?php echo qty_credit?> this is wrong, you're trying to open another php tag on an already open one and you don't use the $ on the variable and then you try to sum the variable so it gives you an error.

"UPDATE avis_credits SET credits='<?php echo qty_credit?> + $qty_credit'";

This will sanitize your input and sum the value of credits with the addition of value of your variable $qty_credit:

$sql = sprintf("UPDATE avis_credits SET credits = credits + '%s'", 
               mysql_real_escape_string($qty_credit));

As a side note, you may want to specify an ID of the account you want to deposit the additional credit otherwise the above rule will increase that credit for ALL rows.

$sql = sprintf("UPDATE avis_credits SET credits = credits + '%s' WHERE id = '%s'", 
               mysql_real_escape_string($qty_credit),
               mysql_real_escape_string($id));

edited Aug 28, 2013 at 9:26

answered Aug 28, 2013 at 9:17

Prix

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1 Comment

Maggie Ackermann Over a year ago

Thank you there is only one row per database so I don't really need to be concerned about the id of the row as no others info or rows set in the database. Your assistance greatly appreciated

Atrakeur · Accepted Answer · 2013-08-28 09:16:56Z

2

SQL support arthmetic operations. So you can do the following:

 "UPDATE avis_credits SET credits=credits + $qty_credit";

answered Aug 28, 2013 at 9:16

Atrakeur

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