Determine if $var in one table and not in other - How?

skeetley

I have a script that prints out the latest conditons for several stations for a given time.

My sql looks like:

$query = "SELECT * FROM ".$product.", Stations WHERE (".$product.".FMFP_ID=Stations.FMFP_ID) AND (Stations.Grp IN(" . stripslashes($choice) . ")) AND (Stations.Forecast LIKE 'y') ORDER by 'Date_Valid' DESC,'Grp','District'";

Now this works fine. But sometimes the data from a station is not in the db when this string page is called. Right now, the station is just skipped as it only prints the stations for which records exist.

What type of idea do I need to implement to get it to print "--" or something for missing stations without having to hard code each station in?

For example, Stations table has:

Station1
Station2
Station3
Station4
Station5

$product table only has records for"
Station1
Station2
Station4

What gets printed is
Station1
Station2
Station4

What I want printed is
Station1

Station2

Station4

So how do I say if the Station# exists in the Stations table, but not in the $product table, do something??

Many, many thanks.

swr

The usual way to do this is with an "outer join", which may or may not be supported in your version of MySQL.

MySQL join syntax (including outer join) is described here:
http://www.mysql.com/doc/en/JOIN.html
At least one of the user comments shows an outer join.