Return each value only once using cfloop query

Question

Hi,
I have some code that dynamically populates a cfselect list and then populates a second list based on those values. Everything seems to be working fine, except that all values are being pulled from the database, and there are duplicates in most cases. For example, value 1S1W diplays in the drop-down menu 10 times, where I would only like it there once.
Is there a way to have one of each value in my list?
<cfif isDefined('form.select_Main_Group')>
    <cfset page.select_Main_Group = form.select_Main_Group>
</cfif>
<cfoutput>
  <form name="DropDown" method="post">
  <!--- query DB for the first drop down list --->
<CFQUERY name="get_Main_Group" datasource="ds" dbtype="odbc">
SELECT *
          FROM  slco_sire.dbo.area_reference_plats_doc INNER JOIN slco_sire.dbo.area_reference_plats_page
          ON    slco_sire.dbo.area_reference_plats_doc.doc_id = slco_sire.dbo.area_reference_plats_page.doc_id
          ORDER BY page_description
</CFQUERY>
  <!--- first drop down list --->
  <!--- NOTICE the onChange javascript event in the select tag, this is what submits the form after the first selection --->
  <select name="select_Main_Group" required="yes" onchange="this.form.submit()">
     <option>Select Township/Range</option>
     <!--- dynamically populate the first drop down list based on the get_Main_Group query --->
     <!--- NOTICE the CFIF within the option tag, this says, if the first selection has been made, display the chosen option when the page reloads --->
     <cfloop query="get_Main_Group">
         <option value="#SECTION#" <cfif isDefined('form.select_Main_Group')><cfif form.select_Main_Group eq "#SECTION#">selected</cfif></cfif>>#TOWNSHIP_RANGE#</option>
           </cfloop>
</select>
<p>
<!--- if the first selection has been made, display the second drop down list with the appropriate results --->
<cfif isDefined('page.select_Main_Group')>
   <!--- query DB for second drop down list, based on the selected item from the first list --->
   <cfquery name="get_Sub_Group" datasource="ds" dbtype="odbc">
        SELECT TOWNSHIP_RANGE, SECTION
        FROM  slco_sire.dbo.area_reference_plats_doc INNER JOIN slco_sire.dbo.area_reference_plats_page
                    ON    slco_sire.dbo.area_reference_plats_doc.doc_id = slco_sire.dbo.area_reference_plats_page.doc_id
        WHERE SECTION = '#page.select_Main_Group#'
   </cfquery>
   <!--- second drop down list --->
   <select name="select_Sub_Group" required="yes">
      <option>Select Section</option>
      <!--- dynamically populate the second drop down list based on the get_Sub_Group query --->
      <cfloop query="get_Sub_Group">
         <option value="#SECTION#">#SECTION#</option>
      </cfloop>
   </select>
</cfif>
</form>
</cfoutput>

Answer 1

Emily,
OK.  Yes it is possible.  Change your first query to:
SELECT  DISTINCT TOWNSHIP_RANGE
          FROM  slco_sire.dbo.area_reference_plats_doc INNER JOIN slco_sire.dbo.area_reference_plats_page
          ON    slco_sire.dbo.area_reference_plats_doc.doc_id = slco_sire.dbo.area_reference_plats_page.doc_id
          ORDER BY TOWNSHIP_RANGE
</CFQUERY>
Notice I removed any mention of SECTION, because it's irrelevant to generating a unique list of TOWNSHIP_RANGE.  Also, GROUP BY is not needed, but an ORDER BY will sort the records in alphanumeric order.
Then you need to modify your code where you generate the option list for the first pulldown:
<option value="#get_Main_Group.TOWNSHIP_RANGE#" <cfif StrucKeyExists(form,'select_Main_Group') AND form.select_Main_Group eq "#get_Main_Group.TOWNSHIP_RANGE#">selected</cfif>>#get_Main_Group.TOWNSHIP_RANGE#</option>
Here I did a couple of things beside changing SECTION references to TOWNSHIP_RANGE .  It's a good idea to add the query name prefix to column names when you output them so that you avoid collisions with variables that have the same name.  I also reduced your <CFIF> statements to one compound statement for simplicity, and replaced the IsDefined with a StructKeyExists function.  This is considered to be better practice and won't throw an error when used in a compound statement (if you kept the IsDefined statement and tried that in a compound selection, it can sometimes throw errors if the variable in the IsDefined doesn't exist).
Now, your second query should be something like:
<cfquery name="get_Sub_Group" datasource="ds" dbtype="odbc">
        SELECT DISTINCT SECTION
        FROM  slco_sire.dbo.area_reference_plats_doc INNER JOIN slco_sire.dbo.area_reference_plats_page
                    ON    slco_sire.dbo.area_reference_plats_doc.doc_id = slco_sire.dbo.area_reference_plats_page.doc_id
        WHERE TOWNSHIP_RANGE = '#page.select_Main_Group#'
        ORDER BY SECTION
   </cfquery>
Here I changed the WHERE clause to filter based on the TOWNSHIP_RANGE you selected in the first pull-down.  This should now return a list of SECTIONs that match the TOWNSHIP_RANGE selected in the first pull-down.
Lastly, some minor changes to the option list for the second pulldown:
  <option value="#get_Sub_Group.SECTION#">#get_Sub_Group.SECTION#</option>
One other thing I noticed.  If you are on ColdFusion 8 or 9, the dbytpe="odbc" is no longer needed.  I'm assuming you are using an ODBC database connection to something like MS Access.  If so, you can omit the dbytype entirely.  It's only needed now if you do query-of-query queries, where it would be dbtype="query".
HTH,
-Carl V.