Using PHP to search a MySQL database and return information.

I am building a directory site with a Joomla component that has a Google Map facility but not up to the high standard and functionality of another map component I am using.

So, to save on work I ask this:

Within the map an info block pops up when you click the marker icon. As with Google Maps. I need information in these blocks. I have the information already in the directory database so do not want to duplicate it. To display the same information in the directory within the map block can I use the following code where it allows me to insert code and add in the relevant information:
$query = $db->getQuery(true);
$query->where($db->nameQuote('this').' = '.$db->quote('that'));
$result = $database->loadResult();
Does this mean I can display information from another table within the same database?

If so, I would like to do display the following:

If the ID of this Marker icon matches the ID of e.g.databaseXYZ, then enter information from databaseabc, column123.

If I can, what is the relevant information and where does it go?