Re: Have: Seq Scan - Want: Index Scan - what am I doing wrong?

On Oct 16, 2012, at 20:01 , Evgeny Shishkin <itparanoia(at)gmail(dot)com> wrote:

> Selecting 5 yours of data is not selective at all, so postgres decides it is cheaper to do seqscan.
>
> Do you have an index on patient.dnsortpersonnumber? Can you post a result from
> select count(*) from patient where dnsortpersonnumber = '347450'; ?
>

Yes, there is an index:

"Aggregate (cost=6427.06..6427.07 rows=1 width=0)"
" -> Index Scan using patient_pracsortpatientnumber on patient (cost=0.00..6427.06 rows=1 width=0)"
" Index Cond: (dnsortpersonnumber = '347450'::text)"

In fact, all the other criteria is picked using an index. I fear that the >= and <= on the timestamp is causing the issue. If I do a "=" of just one of them, I get an index scan. But I need to scan the entire range. I get queries like "give me everything that was entered into the system for this patient between these two dates". A single date wouldn't work.