Обсуждение: count(distinct)

Hi,

this is probably an old issue but I'm not all that experienced.

I wonder if an index can be accessed rather directly, as to speed up
a query like "select count(distinct())", by simply calculating the 
number of branches (leaves) an index has. Or at least to skip sorting.

Best regards, Zdravko

Zdravko Balorda wrote:
> this is probably an old issue but I'm not all that experienced.
> 
> I wonder if an index can be accessed rather directly, as to speed up
> a query like "select count(distinct())", by simply calculating the
> number of branches (leaves) an index has. Or at least to skip sorting.

Afraid not. Have a search of the archives for discussion on "mvcc
visibility indexes" for lots on this.

--  Richard Huxton Archonet Ltd