SELECT station_id, tcl_total, total, a.tcl_total - total as diff

from (

 SELECT station_id, SUM(tcl_missing + tcl_not_missing) AS tcl_total

 FROM tcl_missing_summary 

 GROUP BY station_id

) AS a INNER JOIN

​

(

 SELECT station_id, SUM(total) AS total

 FROM tcl_breakdown_op

 WHERE tr_standard NOT LIKE '%cru'

 GROUP BY station_id

) AS b

ON a.stationid = b.stationid

 WHERE a.tcl_total - total <> 0