Kenneth Marshall <k...@rice.edu> writes:
> On Thu, Dec 23, 2010 at 10:42:26PM +0800, Li Jie wrote:
>> But in the last query that sorts on "id", since the query selects all the
>> columns for output, the actual sorted size is the same, and the only
>> difference is the comparison cost. The query sorting on two columns needs to
>> do twice the comparison. Am I right?
> I think you are right. Sorry for the confusion.
I doubt the cost of comparing two integers is the issue here; rather
it's more likely one of how many merge passes were needed. You could
find out instead of just speculating by turning on trace_sort and
comparing the log outputs.
regards, tom lane
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