google is your best friend.
in action:
source code:
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<html>
<head>
<title>Related cfselects</title>
</head>
<body>
<cfscript>
state = queryNew("stateid,name");
queryAddRow(state);
querySetCell(state, 'stateid','1');
querySetCell(state, 'name','California');
queryAddRow(state);
querySetCell(state, 'stateid','2');
querySetCell(state, 'name','New York');
queryAddRow(state);
querySetCell(state, 'stateid','3');
querySetCell(state, 'name','Arizona');
queryAddRow(state);
querySetCell(state, 'stateid','4');
querySetCell(state, 'name','Illinois');
city = queryNew("stateid,name,cityid");
addRow(city, '1','Laguna Beach','LB' );
addRow(city, '1','Los Angeles','LA' );
addRow(city, '1', 'Newport Beach', 'NB');
addRow(city, '1', 'San Francisco' ,'SF');
addRow(city, '1', 'San Diego' ,'SD');
addRow(city, '2', 'Manhattan' ,'M');
addRow(city, '2', 'Brooklyn' ,'B');
addRow(city, '3', 'Phoenix' ,'P');
addRow(city, '3', 'Elgin' ,'E');
addRow(city, '3', 'Tucson' ,'T');
addRow(state, '4','Chicago', 'C');
function addRow( rs, stateid, name, cityid)
{
queryAddRow(city);
querySetCell(city,'stateid',stateid);
querySetCell(city,'name',name);
querySetCell(city,'cityid',cityid);
}
</cfscript>
<cfsavecontent variable="actionPopulate">
if(_global.arrCities == undefined) _global.arrCities = selectCity.dataProvider.slice(0);
var arrCities:Array = _global.arrCities;
selectCity.removeAll();
for(var i = 0; i < arrCities.length; i++)
{
var item = arrCities
.data.split('|');
if(item[1] == selectState.value )
{
selectCity.addItem(arrCities.label,item[0]);
}
}
selectCity.enabled = (selectCity.length >0) ? true:false;
</cfsavecontent>
<cfform name="myform" format="flash" width="400">
<cfformgroup type="hbox">
<cfselect queryposition="below" label="State"
name="selectState" query="state" value="stateid"
display="name" width="200"
onChange="#actionPopulate#">
<option>Please select a parent category</option>
</cfselect>
<cfselect queryposition="below" disabled="true" label="City"
name="selectCity" width="200">
<cfoutput query="city"><option value="#cityid#|#stateid#">#name#</option></cfoutput>
</cfselect>
</cfformgroup>
</cfform>
</body>
</html>