Re: No heap lookups on index

On Thu, Jan 19, 2006 at 10:19:01AM -0800, Josh Berkus wrote:
> One of the other most valuable targets for index-only access is the 
> "many-to-many join table" whose primary key consists of two (or more) 
> foreign keys to two (or more) other tables.  It's actually not necessary 
> to check visibility on this kind of table as the visibility of tuples in 
> the join table will be determined by the visibility of tuples in the two 
> data tables.  Since often join tables consist *only* of the join key, 
> being able to do index-only access on them could dramatically speed up 
> certian kinds of queries.

How would that handle 'delinking' item A from foobaz 2? (IE: DELETE FROM
join_table WHERE id1=231 and id2=24842)

The only way I can see this working is if it is required that items in
both tables as well as the link in the many-many table are only inserted
and deleted in the same transaction, which seems to be really pushing
this into corner-case territory.
-- 
Jim C. Nasby, Sr. Engineering Consultant      jnasby@pervasive.com
Pervasive Software      http://pervasive.com    work: 512-231-6117
vcard: http://jim.nasby.net/pervasive.vcf       cell: 512-569-9461