Ahh yes, thanks for finding that off-by-one situation. Your query is
nearly identical to one from Tomasz Myrta.
Seq Scan on clp (cost=0.00..2.26 rows=34 width=6) (actual
time=7.98..11.42 rows=400 loops=1) Filter: (commit_date < $0) InitPlan -> Limit (cost=5.62..5.62 rows=1 width=8)
(actualtime=7.29..7.31
rows=1 loops=1) -> Sort (cost=5.37..5.62 rows=101 width=8) (actual
time=6.49..6.90 rows=101 loops=1) Sort Key: commit_date -> Seq Scan on clp
(cost=0.00..2.01rows=101 width=8)
(actual time=0.21..3.73 rows=500 loops=1)Total runtime: 15.36 msec
(8 rows)
On Fri, 28 Feb 2003, Robert Treat wrote:
> delete from clp where commit_date < (select commit_date from clp order
> by commit_date offset 99 limit 1);
>
> Robert Treat
>
> On Fri, 2003-02-28 at 12:16, Dan Langille wrote:
> > Hi folks,
> >
> > I wanted to delete "old" rows from a table. These are the rows I
> > want to keep:
> >
> > SELECT *
> > FROM clp
> > ORDER BY commit_date
> > LIMIT 100
> >
> > So I tried this:
> >
> > DELETE FROM clp
> > WHERE NOT EXISTS (
> > SELECT *
> > FROM clp
> > ORDER BY commit_date
> > LIMIT 100);
> >
> > Uhh uhh, nothing deleted. I don't understand why.
> >
> > OK, I can do this instead:
> >
> > DELETE from clp
> > where commit_log_id NOT in (
> > SELECT commit_log_id
> > FROM clp
> > ORDER BY commit_date
> > LIMIT 100);
> >
> > Can you think of a better way?
> > --
> > Dan Langille : http://www.langille.org/
> >
> >
> > ---------------------------(end of broadcast)---------------------------
> > TIP 5: Have you checked our extensive FAQ?
> >
> > http://www.postgresql.org/users-lounge/docs/faq.html
>
>
>
>
