Re: Index on parent/child hierarchy

On Wed, Jan 25, 2012 at 11:54 AM, Jason Armstrong <ja(at)riverdrums(dot)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?

Something like this...

WITH RECURSIVE subtree(depth, id, parent, type_id) AS (
SELECT 0, id, parent, type_id FROM uuid.master WHERE id = X
UNION
SELECT depth+1, m.id, m.parent, m.type_id
FROM subtree t, uuid.master m
WHERE m.parent = t.id
)
SELECT count(*)
FROM subtree
WHERE type_id = 4;

Add an index on id

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