[BUGS] Re: Query planner skipping index depending on DISTINCT parameterorder (2)

On 17 September 2017 at 18:15, Tom Lane <tgl@sss.pgh.pa.us> wrote:

> For plain DISTINCT, yeah we could consider other orderings ... but
> we're rather unlikely to find an index that matches all the output
> columns, regardless of what order they're in.  So it's just not that
> exciting.

I don't follow this part. Are you saying a simple "select distinct a,b
from table" is unlikely to find a matching index on <b,a>? Don't we
already do exactly this for "select a,b from table group by a,b"? I
would have expected the two equivalent SQL statements to use exactly
the same infrastructure and thought it was only a matter of historical
legacy that they didn't.

-- 
greg


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