On Wed, Jan 25, 2012 at 5:54 AM, Jason Armstrong <ja@riverdrums.com> wrote:
> Hi
>
> I'm looking for advice on the best way to index a table that is defined as:
>
> create table uuid.master(id uuid, parent uuid references
> uuid.master(id), type_id smallint, primary key(id));
>
> Besides the primary key, I have these two indices on the table too:
> CREATE INDEX master_parent_idx ON uuid.master(parent);
> CREATE INDEX master_type_idx ON uuid.master(type_id);
>
> I have data arranged in four levels (ie type_id is from 1 to 4):
>
> 1. id=A type_id=1
> 2. id=B parent=A type_id=2
> 3. id=C parent=B type_id=3
> 4. id=D parent=C type_id=4
> 2. id=E parent=A type_id=2
> 3. id=F parent=E type_id=3
> 4. id=G parent=F type_id=4
> 4. id=H parent=F type_id=4
> 4. id=I parent=F type_id=4
> 3. id=J parent=E type_id=3
> 4. id=K parent=J type_id=4
>
> I want to count all type_id=4 for a particular type_id=1 uuid.
>
> I use this query:
>
> SELECT count(t4.id)
> FROM uuid.master AS t4
> INNER JOIN uuid.master AS t3 ON t4.parent=t3.id
> INNER JOIN uuid.master AS t2 ON t3.parent=t2.id
> INNER JOIN uuid.master AS t1 ON t2.parent=t1.id
> WHERE t1.id=UUID
>
> Apart from creating a separate table to keep track of the counts, is
> there a good way to index the table to help?
If your data is organized as a tree, tends to run deep (causing many
recursion joins), and you often make sweeping subset operations
starting from a parent node, and your data isn't too heavily updated,
you might want to consider materialized path organization instead of
parent/child. Both arrays and strings work for that.
id=I parents=A,E,F type_id=4
SELECT count(*) FROM uuid.master WHERE parents LIKE 'A,E%' and type_id = 4;
The point here is that you can exploit the tree structure with a btree
index. Before we got recursive queries, this was often the best way
to do it, but now it's kind of a niche solution to be used when
certain things fall into place.
merlin