try with below script and put on field mapping script to get the location unique value .
First identify which column will be always going to be unique , apply the coalesce on that column, if you have reference field that will always going to be unique, apply that on reference field.
Note: this is a sample code, but you can make the changes based on your need.
answer = (function transformEntry(source) {
var comp = new GlideRecord('cmn_location');
comp.addQuery('name', '=', source.u_location);
comp.addQuery('state', '=', source.u_state___province);
comp.addQuery('country', '=', source.u_country);
comp.query();
if (comp.next()) {
return comp.sys_id;
}
})(source);
