Re: Self referencing composite datatype

>
> On Wed, Aug 7, 2013 at 4:57 AM, Sameer Thakur <samthakur74(at)gmail(dot)com>wrote:
>
>> Hello,
>> I wanted to create a composite datatype to represent a Node. So it would
>> have a few attributes and an array of type Node which is the children of
>> this node.
>> create type Node as (r integer, s integer, children Node []);
>> But i get error type Node[] does not exist. I understand that Node is not
>> defined hence the error.
>> But how do i get around this problem?
>>
>
> What exactly are you trying to accomplish? I can think of a number of
> ways.
>
> For example, suppose we have a table like:
>
> create table node (
> id int primary key,
> parent int references node(id),
> content text not null
> );
>
> We could create a function like this:
>
> CREATE FUNCTION children(node) RETURNS node[] LANGUAGE SQL AS
> $$
> SELECT array_agg(node) FROM node WHERE parent=$1.id;
> $$;
>
> Then we could still do:
>
> select n.children FROM node n WHERE id = 123;
>
> Note that causes two separate scans, but should work.
>
>
Thank you.
I am trying to capture plan statistics for every node in the plan tree. For
this i have plan view which has plan specific information like
planid,plan_text, and root_node of type Node.

Type Node has node specific statistics like estimated_startup_cost,
estimated_actual_cost etc. It also has child_nodes of type Node[]. i face
the problem of self referencing composite type in defining Node type.

The reason i wanted a type Node is because while initializing memory for my
contrib module i have GUC parameter specifying max number of Nodes. I was
thinking that it is possible to initialize memory with a sizeof(Node).

Still trying to figure out how using a table storing Node will help me in
figuring out how much initial memory can be allocated

regards
Sameer