Re: dumb question

On Thu, Jun 2, 2016 at 4:11 PM, John R Pierce <pierce(at)hogranch(dot)com> wrote:

> On 6/2/2016 11:10 AM, Steve Clark wrote:
>
> Thanks all the below seem to do the trick.
>
> On 06/02/2016 01:58 PM, David G. Johnston wrote:
>
> select max(id) from yourtable where sts=0 and id not in (select ref_id
> from yourtable);
>
>
> select max(id) from yourtable where sts=0 and id not in (select ref_id
> from yourtable);
>
>
> do note, this is whats known as an 'anti-join', and these can be pretty
> expensive on large tables.
>
​+1
​

​Though I suspect that with a partial index on (id, sts=0) and (ref_id,
ref_id IS NOT NULL), though highly sensitive to density, that even for
large​ total row counts it would perform pretty well; but I'm not
knowledgeable in how smart we are here. Selecting, in descending order,
(id where sts = 0), from the index and then poking into index(ref_id)
should, particularly if the cross-set is sparse, pretty quickly find a
non-match.

David J.