PHP/MySQL:How: If exist - Update record. If new data - Insert

[leechyeah]

Dear,

I am new to PHP and MySQL.
I have a simple order form on my site: 1 column with "member" and one with "comment".
I am able to Insert rows when a user submits the form.
But when a user wants to modify that data, the form inserts another row - no good.

I want the returning user, to be able to their UPDATED record - not INSERTED again.
I can detect if they have previously submitted an record to the MySQL:

if(mysql_num_rows($replacing) !== 0);
	{
           echo "You have already submitted an order, you may modify this.";

I am stuck now, please help.

Thanks in advance,

Leech

[simplypixie]

Could really do with seeing the rest of your code (especially what you are doing before the piece of code you have already posted). However, as a start, you don't need 2 equals signs and you have put a semi-colon in your if statement which is incorrect, so should be

if (mysql_num_rows($replacing)!=0) { echo........; }

or you could use greater than:

if (mysql_num_rows($replacing)>0) { echo........; }

[leechyeah]

Thanks for your reply.
I managed to get it all working now! Not sure if it is the best way:

$sql = "UPDATE table SET col1 = '$var1', col2 = '$var2' WHERE `user` ='username1' " or die("We have encountered an error:" . mysql_error());

The variables are the $_POST that are sent from a form to the database.

I had a look at this site, but did not make any sense to me: (might be helpful for others)
http://dev.mysql.com/doc/refman/5.0/en/insert-on-duplicate.html

Also this is very helpful to my solution:
http://phpeasystep.com/mysql/9.html

Thanks to all