On Tue, 2005-11-29 at 20:58, John D. Burger wrote:
> I could use some help with the following:
>
> I have a database of geographic entities with attributes spread across
> several tables. I need to determine which entities are unique with
> respect to some of those attributes. I'm using the following query:
>
> select p2.gazPlaceID from
> (select p1.featureType, n1.placeNameID, c1.containerID
> from gazPlaces as p1
> join gazNamings as n1 using (gazPlaceID)
> join gazContainers as c1 using (gazPlaceID)
> group by p1.featureType, n1.placeNameID, c1.containerID
> having count(*) = 1) as uniqs,
> gazPlaces as p2
> join gazNamings as n2 using (gazPlaceID)
> join gazContainers as c2 using (gazPlaceID)
> where uniqs.featureType = p2.featureType
> and uniqs.placeNameID = n2.placeNameID
> and uniqs.containerID = c2.containerID;
>
> The basic idea is to compute featureType-placeNameID-containerID
> combinations with a three-way join, determine which of those have a
> count of 1, and then join that back to the same three-way join to get
> the gazPlaceIDs corresponding to the unique combos (whew!).
>
> gazPlaces has about 6M entries, gazNamings and gazContainers each about
> 10M. All of the fields above are integers, and I have indexes on
> everything relevant, but the query still takes about eight hours. My
> question is not (necessarily) how to improve the efficiency of this
> query, but whether anyone can think of a faster way to compute the
> uniques. Again, the goal is to find entries in gazPlaces that are the
> only ones with their particular combination of feature type, name and
> container.
OK, let's assume that the basic part of it, before the group by, has
been put into a view, so we can then do:
select pkey1, field2, field3, field4 from view;
And we know that pkey1 is unique, but we want the records where pkey1 is
the only thing different between them, right?
select
v1.pkey1,
v1.field2,
v1.field3,
v1.field4,
v2.pkey1,
v2.field2,
v2.field3,
v2.field4,
from
view v1
join
view v2
on (
v1.field2=v2.field2 and
v1.field3=v2.field3 and
v1.field3=v2.field3 and
v1.pkey1<>v2.pkey
)
How does that work?
