Re: sql to delete rows from joining a table to itself
Date: Mon, 29 Jun 2009 09:41:50 -0700 (PDT)
On Jun 29, 7:03 am, Ed Prochak <edproc..._at_gmail.com> wrote:
> On Jun 28, 7:51 pm, Jeff Calico <jeffcal..._at_gmail.com> wrote:
> > Hello everyone
> > I am trying to delete rows from a massive data table that are "almost"
> > duplicates. I can do a nice query
> > to find them when I join the table with itself, but I can't figure out
> > how to form a delete statement out
> > of this.
> > Query:
> > SELECT a.*
> > FROM Trafficdata a, Trafficdata b
> > WHERE a.id = b.id
> > AND a.date = b.date
> > AND a.flag = 'Q'
> > AND b.flag = 'Q'
> > AND a.dstop = b.dstop
> > AND (a.batch != b.batch OR (a.batch = b.batch AND a.pos_marker <
> > b.pos_marker) );
> > One idea I tried after searching the web was
> > DELETE FROM ( <above query> ); but that gives
> > ORA-01752 "Cannot delete from view without exactly one key preserved
> > table"
> > Any help would be greatly appreciated!
> > Jeff C.
> Do you have a primary key on this Trafficdata table?
> Assuming your results are the rows your really want to delete then a
> delete of the form:
> DELETE FROM Trafficdata WHERE pk IN (SELECT a.pk from ...) ;
> I suggest you do this AFTER doing a backup.
Thanks for your reply. No, there isn't don't have a primary key on this data table. I also can't make a backup of the TrafficData table, due to its huge size, but I did make a smaller table to experiment on.
Jeff Received on Mon Jun 29 2009 - 11:41:50 CDT