Column 'county' in where clause is ambiguous - error when adding 'DataAssist Search Behaviour'

OK so I have just realised that the problem lied with the two tables ( properties, agents ) being used in the recordset both have a column named 'county'. So I changed the 'county' column in the 'agents' table to 'county_a'. which solved the error.

What I don't understand is the 'county' column from the 'agents' table wasn't being selected in the recordSet. as below -

mysql_select_db($database_Testing_server, $Testing_server);
$query_rsRTMs = "SELECT properties.property_id, properties.property_name, properties.address, properties.town_city, properties.county, properties.`size`, properties.type, properties.acquisition, properties.image, properties.agent_id, properties.alt_tag, properties.title_tag, agents.agent_id, agents.name, agents.url FROM properties, agents WHERE properties.agent_id = agents.agent_id ORDER BY properties.acquisition ASC";
setQueryBuilderSource($query_rsRTMs,$WADbSearch1,false);
$rsRTMs = mysql_query($query_rsRTMs, $Testing_server) or die(mysql_error());
$row_rsRTMs = mysql_fetch_assoc($rsRTMs);
$totalRows_rsRTMs = mysql_num_rows($rsRTMs);

So how is it appearing in the column list from the filter options?

Filter is now working. using the following repeat region to filter the 'county' column.

// RepeatSelectionCounter_2 Begin Loop
$RepeatSelectionCounter_2_IterationsRemaining = $RepeatSelectionCounter_2_Iterations;
while($RepeatSelectionCounter_2_IterationsRemaining--){
if($RepeatSelectionCounterBasedLooping_2 || $row_rsCounty){
?>
<li><a href="right-to-manage-success-t.php?county=<?php echo $row_rsCounty['county']; ?>"><?php echo $row_rsCounty['county']; ?></a></li>
<?php
} // RepeatSelectionCounter_2 Begin Alternate Content
else{
?>
<?php } // RepeatSelectionCounter_2 End Alternate Content
if(!$RepeatSelectionCounterBasedLooping_2 && $RepeatSelectionCounter_2_IterationsRemaining != 0){
if(!$row_rsCounty && $RepeatSelectionCounter_2_Iterations == -1){$RepeatSelectionCounter_2_IterationsRemaining = 0;}
$row_rsCounty = mysql_fetch_assoc($rsCounty);
}
$RepeatSelectionCounter_2++;
} // RepeatSelectionCounter_2 End Loop
?>

I now want to use a second repeat region to filter the 'agents' column.

I think I need to hand code this just not sure how.

Current page attached

Thanks in advance.