explain analyze SELECT t4.detectorid, t4.description, t4.count, total,
       CAST(t4.count AS NUMERIC) / CAST(total AS NUMERIC) * 100.0 AS percentage
FROM  (SELECT t1.detectorid, description, count(*) as count
        from loopdata_2007_01_01 t1, loop_status
        where t1.status = loop_status.status
        GROUP BY t1.detectorid, description) t4,
     (SELECT detectorid, COUNT(*) AS total
      FROM loopdata_2007_01_01 t2
      GROUP BY detectorid
      ORDER BY detectorid) t3
WHERE t4.detectorid = t3.detectorid
ORDER BY t4.detectorid, t4.description, t3.total
;
                                                                              QUERY PLAN
-----------------------------------------------------------------------------------------------------------------------------------------------------------------------
 Sort  (cost=710083.07..711078.47 rows=398161 width=38) (actual time=22667.435..22668.159 rows=1386 loops=1)
   Sort Key: t1.detectorid, loop_status.description, t3.total
   Sort Method:  quicksort  Memory: 198kB
   ->  Merge Join  (cost=602939.70..651271.14 rows=398161 width=38) (actual time=17907.248..22665.778 rows=1386 loops=1)
         Merge Cond: (t1.detectorid = t3.detectorid)
         ->  GroupAggregate  (cost=544650.66..573487.36 rows=126200 width=22) (actual time=14246.234..18997.411 rows=1386 loops=1)
               ->  Sort  (cost=544650.66..551465.46 rows=2725920 width=22) (actual time=14242.307..17137.123 rows=2725920 loops=1)
                     Sort Key: t1.detectorid, loop_status.description
                     Sort Method:  external merge  Disk: 50000kB
                     ->  Hash Join  (cost=45.33..85556.32 rows=2725920 width=22) (actual time=0.076..5438.041 rows=2725920 loops=1)
                           Hash Cond: (t1.status = loop_status.status)
                           ->  Seq Scan on loopdata_2007_01_01 t1  (cost=0.00..44622.20 rows=2725920 width=4) (actual time=0.032..1685.744 rows=2725920 loops=1)
                           ->  Hash  (cost=25.70..25.70 rows=1570 width=22) (actual time=0.030..0.030 rows=6 loops=1)
                                 ->  Seq Scan on loop_status  (cost=0.00..25.70 rows=1570 width=22) (actual time=0.016..0.021 rows=6 loops=1)
         ->  Materialize  (cost=58289.03..58303.23 rows=631 width=10) (actual time=3660.990..3663.363 rows=1386 loops=1)
               ->  Subquery Scan t3  (cost=58289.03..58296.92 rows=631 width=10) (actual time=3660.983..3662.162 rows=631 loops=1)
                     ->  Sort  (cost=58289.03..58290.61 rows=631 width=2) (actual time=3660.980..3661.429 rows=631 loops=1)
                           Sort Key: t2.detectorid
                           Sort Method:  quicksort  Memory: 54kB
                           ->  HashAggregate  (cost=58251.80..58259.69 rows=631 width=2) (actual time=3659.995..3660.390 rows=631 loops=1)
                                 ->  Seq Scan on loopdata_2007_01_01 t2  (cost=0.00..44622.20 rows=2725920 width=2) (actual time=0.044..1633.167 rows=2725920 loops=1)
 Total runtime: 22686.007 ms
(22 rows)