Re: Stats for multi-column indexes

Simon Riggs wrote:
> On Tue, 2007-03-20 at 14:14 +1200, Mark Kirkwood wrote:
>> Jeff Davis wrote:
>>> I know we can't keep stats on every combination of columns. My initial
>>> idea would be to only keep stats about a multi-column index (and
>>> probably optional for those, too).
>>>
>> Maybe you would want to keep single column indexes too, so that (more) 
>> accurate estimates for bitmap-and type plans are possible.
> 
> We should allow the DBA to specify which groups of cols to keep
> statistics on, if there is no index on that group.
> 
> That solves the combinatorial explosion problem.

This is one hint I think everyone can agree on. Being able to say that 
values in different columns are related just gives the planner more 
information to work with.

--   Richard Huxton  Archonet Ltd