Hi Thiemo,
On 07/01/2019 11:30, Thiemo Kellner wrote: > > Hi HP > > Thanks for your reply. > > Quoting "Peter J. Holzer" <hjp-pg...@hjp.at>: > >> On 2018-12-25 11:54:11 +0000, Thiemo Kellner wrote: >> [three different but functionally equivalent queries] >> >>> Explain analyze verbose showed for: >>> A (cost=264.72..626.97 rows=31 width=90) (actual time=1.117..1.117 rows=0 >>> loops=1) >>> C (cost=0.42..611.19 rows=31 width=52) (actual time=2.217..2.217 rows=0 >>> loops=1) >> >> 626.97 doesn't seem "much higher" to me than 611.19. I would call that >> "about the same". >> > > So would I but the cost is given as a range. Taking the the average somewhat > 400 compare to somewhat 300. I do not know whether averaging is appropriate > here. The cost is not a range. The 2 numbers you see are: * Estimated start-up cost. This is the time expended before the output phase can begin, e.g., time to do the sorting in a sort node. * Estimated total cost. This is stated on the assumption that the plan node is run to completion, i.e., all available rows are retrieved. In practice a node's parent node might stop short of reading all available rows (see the LIMIT example below). As you can read here: https://www.postgresql.org/docs/current/using-explain.html regards, fabio pardi