[gato-gordo]

Hey, thanks. That final solution sorts some more of the compound last names correctly, but takes people that have added a middle initial to their first name out of order. E.g., Linda C. Floyd gets sorted as a ‘C’.

Does anyone know how to do this with the wp_usermeta.last_name or know why the code I posted breaks those functions?

[gato-gordo]

Thanks, in case people want to know what the query looks like for something like this:

$query_string = $_SERVER['QUERY_STRING']; 

if(isset($query_string)){

  parse_str($query_string, $query_array);
		
  $letter = $query_array['Last_name_first_letter'];
}

if(isset($letter)){
  $the_field = xprofile_get_field_id_from_name('Last Name');
  $custom_ids = $wpdb->get_col("SELECT user_id FROM {$wpdb->prefix}bp_xprofile_data WHERE field_id = $the_field AND LEFT(value, 1) = '" . $letter . "' ");
}