Re: [SQL] Perfomance benefit using Min() against order by & limit 1?

[Fernando Hevia]

Oops. Previous message went in HMTL. Sorry for that.
Text-only version follows.

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Hi guys. Is there any difference between these two queries regarding
performance?
Table stopvoip has several million records. 
I suspect using the aggregate function would be best, but benchmarking
doesn’t seem to confirm it. Both queries take around 150 - 175 ms once data
has been cached. 
Any hindsights?

SELECT min(h323setuptime::date)
FROM stopvoip 
WHERE callingstationid = '2941605118'   
AND h323setuptime >= '2007.07.01'   
AND h323disconnectcause = '10'   
AND acctsessiontime > 0   
AND NOT calledstationid ~ '^99[89]#'   

Aggregate  (cost=11151.25..11151.27 rows=1 width=8)"
  ->  Bitmap Heap Scan on stopvoip  (cost=29.29..11149.98 rows=507 width=8)
        Recheck Cond: ((callingstationid)::text = '2941605118'::text)
        Filter: ((h323setuptime >= '2007-07-01 00:00:00-03'::timestamp with
time zone) AND ((h323disconnectcause)::text = '10'::text) AND
(acctsessiontime > 0) AND ((calledstationid)::text !~ '^99[89]#'::text))
        ->  Bitmap Index Scan on idx_stopvoip_callingid2  (cost=0.00..29.29
rows=2939 width=0)
              Index Cond: ((callingstationid)::text = '2941605118'::text)


SELECT h323setuptime::date 
FROM stopvoip 
WHERE callingstationid = '2941605118'   
AND h323setuptime >= '2007.07.01'   
AND h323disconnectcause = '10'   
AND acctsessiontime > 0   
AND NOT calledstationid ~ '^99[89]#'   
ORDER BY 1 
LIMIT 1

Limit  (cost=11174.03..11174.03 rows=1 width=8)
  ->  Sort  (cost=11174.03..11175.30 rows=507 width=8)
        Sort Key: (h323setuptime)::date
        ->  Bitmap Heap Scan on stopvoip  (cost=29.29..11151.25 rows=507
width=8)
              Recheck Cond: ((callingstationid)::text = '2941605118'::text)
              Filter: ((h323setuptime >= '2007-07-01 00:00:00-03'::timestamp
with time zone) AND ((h323disconnectcause)::text = '10'::text) AND
(acctsessiontime > 0) AND ((calledstationid)::text !~ '^99[89]#'::text))
              ->  Bitmap Index Scan on idx_stopvoip_callingid2 
(cost=0.00..29.29 rows=2939 width=0)
                    Index Cond: ((callingstationid)::text =
'2941605118'::text)


Thanks,
Fernando.


---------------------------(end of broadcast)---------------------------
TIP 9: In versions below 8.0, the planner will ignore your desire to
       choose an index scan if your joining column's datatypes do not
       match