single-rank_math_locations.php

<?php
/*
* We are using rank_math_locations custom post type. (or any other)
* Meta Box to create custom fields which saves in its own database table
* We have location metabox custom field saved in table "mbox_locations" and 
* service type custom field saved in table "mbox_services"
* 
* mbox_locations contains a sub-field(toggle) called capital-cities
* mbox_services contains a sub-field(radio) called service-type
*/
//get all rank-math-locations where "capital cities" is toggled ON and service-type is "plumbing"
global $wpdb;
$locations_sql   = "SELECT mbox_locations.ID " .
                   "FROM mbox_services, mbox_locations " .
                   "WHERE " .
                   "mbox_locations.capital_cities = 1 AND " .
                   "mbox_services.service_type  LIKE '%plumbing%' AND " .
                   "mbox_locations.ID = mbox_services.ID;";
$locations_ids   = $wpdb->get_col( $locations_sql );
$locations_args  = array(
  'post__in'  => $locations_ids,
  'post_type' => 'rank_math_locations',
);
$locations_query = new WP_Query( $locations_args );
if ( $locations_query->have_posts() ) {
  while ( $locations_query->have_posts() ) {
    $locations_query->the_post();
    the_title();
  }
} 
?>