Machine_id in meter table - change to using serial_number


/*Last Synch Date */
SELECT 	DATE_FORMAT(max( mtr.date_timestamp),'%m/%d/%Y') as created_date
FROM Y2017_floorplan_machines fpm
INNER JOIN Y2017_floorplans fp ON fpm.floorplan_id = fp.id /*Changed to INNER JOIN*/
INNER JOIN Y2017_buildings bd ON fp.building_id = bd.id /*Changed to INNER JOIN*/
/*LEFT OUTER JOIN Y2018_organization org ON bd.org_id = org.id Not needed for join. org_id is in buildings table*/
#INNER JOIN Y2017_meter mtr ON fpm.id = mtr.machine_id /*This is faster because of pk index. Serial_number is not a pk index*/ 
INNER JOIN Y2017_meter mtr ON fpm.serial_number = mtr.serial_number /*Changed to INNER JOIN*/
    AND mtr.date_timestamp = (SELECT max( i.date_timestamp) FROM Y2017_meter i WHERE i.machine_id = fpm.id and black_meter > 0)
where bd.id =4;