addition of elements in a database

Krista2882

I was wondering if someone could help me out with the PHP code to be able to add together certain elements of a columns of a table in a database.
here's a piece of code that I have written so far:

<?php
$printr = mysql_query("SELECT totalSpent FROM project1 WHERE Preferences = 'rap' ");
while($row = mysql_fetch_array($printr)){
//this is where i'm stuck on how to add the elements together
}
?>

thanks in advance for your help!

laserlight

Are you adding between columns, or rows?

Krista2882

i have a column that contains the amount of money spent on music for each person listed in the database. there is also a column for what type of music each person listens to. so what i need to do is to choose the rows for the people who listen to rap, for example, and then add up the amount that is in the "totalAmount" colums for just the rows pertaining to rap music.

laserlight

Create a variable, say $total, and set it to 0.
Then add $row['totalSpent'] to it on each iteration.

Conversely, you can try a
SELECT SUM(totalSpent) AS total FROM project1 WHERE Preferences = 'rap'
and then just get the value of $row['total'] once.

Krista2882

Ok, I tried that (I knew it must have been something easy like that), but I get an error...

here's what I had changed the code to:

<?php
$total = 0;
$printr = mysql_query("SELECT totalSpent FROM project1 WHERE Preferences = 'rap' ");
while($row = mysql_fetch_array($printr)){
$total = $total + $row['totalSpent'];
}

and this is the error I get:
Warning: mysql_fetch_array(): supplied argument is not a valid MySQL result resource in c:\program files\apache group\Apache\htdocs\Project1.php on line 48

(line 48 is this line: while($row = mysql_fetch_array($printr)){

any ideas?
thanks again!

laserlight

Did you connect to the database server, say by using [man]mysql_connect/man?
Did you select a database, say by using [man]mysql_select_db/man?

Is your query correct?
Check with a

$printr = mysql_query("SELECT totalSpent FROM project1 WHERE Preferences = 'rap' ")
	OR die(mysql_error());

Krista2882

yes, i had done the first two- the other parts of my code worked, so I knew that was all working. So i tried that "OR die(mysql_eror())" thing, and that told me the problem and was able to fix that (I was using the wrong spelling of the column name. :rolleyes: ).
So, thanks a lot for your help with that!