Re: Finding matching columns from two tables

On Thu, 21 Feb 2002 14:34:59 -0800
Richard Emberson <emberson(at)phc(dot)net> wrote:

> Below can be included in a psql via the \i command.

I have lost sight of this mail -- especially detailed explanation annotated
on it. Judging from these examples, my previous queries wouldn't work correctly.
Anyway I have made several modifications on them.

select org2.group_set_id
from (select org0.group_id, org0.group_set_id
from organizations as org0
where exists
(select mem0.group_id
from membership as mem0
where org0.group_id = mem0.group_id
and mem0.user_id = <<input parameter>>
)
and not exists
(select org1.group_id, org1.group_set_id
from organizations as org1
where not exists
(select mem1.group_id
from membership as mem1
where org1.group_id = mem1.group_id
and mem1.user_id = <<input parameter>>
)
and org0.group_set_id = org1.group_set_id
)
) as org2
group by org2.group_set_id
;

Regards,
Masaru Sugawara

> ----------------------------------------------------------------
> /*
> In some cases, the group_ids associated with a group_set_id are the
> same as the group_ids associated with a user_id. For a given user_id
> determine if there is a corresponding group_set_id.
>
> Find the group_set_id such that for a given user_id (input parameter)
> there is a one-to-one correspondence between the group_ids associated
> with the user_id and the group_ids associated with the group_set_id;
> for every group_id that the user_id has, the group_set_id also has it
> and for every group_id that the group_set_id has, the user_id also has
> it.
> If there is no such group_set_id, then return null.
>
> What query will generate the group_set_id?
>
> The function get_group_set_id() is my attempt. Is there a better way?
> The fact that it has 4 SELECT statement in it is, I expect, far from
> optimum.
>
> SELECT get_group_set_id(10); -- should be 30
> SELECT get_group_set_id(11); -- should be -1
> SELECT get_group_set_id(12); -- should be -1
> SELECT get_group_set_id(13); -- should be 31
> */
>
> -- all of the users
> -- user_id are unique
> DROP TABLE users;
> CREATE TABLE users (
> user_id BIGINT,
> -- other columns
> PRIMARY KEY (user_id)
> );
> COPY users FROM stdin USING DELIMITERS ':';
> 10
> 11
> 12
> 13
> \.
>
> -- all of the groups
> -- user_id are unique
> DROP TABLE groups;
> CREATE TABLE groups (
> group_id BIGINT,
> -- other columns
> PRIMARY KEY (group_id)
> );
> COPY groups FROM stdin USING DELIMITERS ':';
> 20
> 21
> 22
> 23
> 24
> \.
> -- a user can be a member of one or more groups
> DROP TABLE membership;
> CREATE TABLE membership (
> user_id BIGINT,
> group_id BIGINT,
> -- other columns
> FOREIGN KEY (user_id) REFERENCES users (user_id),
> FOREIGN KEY (group_id) REFERENCES groups (group_id)
> );
> COPY membership FROM stdin USING DELIMITERS ':';
> 10:20
> 10:21
> 11:20
> 12:21
> 12:22
> 12:23
> 13:20
> 13:22
> \.
>
> -- a group set is a set of one or more groups
> DROP TABLE group_sets;
> CREATE TABLE group_sets (
> group_set_id BIGINT,
> group_id BIGINT,
> -- other columns
> FOREIGN KEY (group_id) REFERENCES groups (group_id)
> -- FOREIGN KEY (group_set_id) REFERENCES group_sets (group_set_id)
> );
> COPY group_sets FROM stdin USING DELIMITERS ':';
> 30:20
> 30:21
> 31:20
> 31:22
> 32:20
> 32:21
> 32:22
> 32:24
> \.CREATE OR REPLACE FUNCTION get_group_set_id (
> BIGINT
> )
> RETURNS BIGINT AS '
> DECLARE
> -- parameters
> user_id_p ALIAS FOR $1;
> -- local variables
> group_id_count_v INTEGER;
> count_v INTEGER;
> group_set_id_v BIGINT;
> foo group_sets%ROWTYPE;
> BEGIN
> -- how many groups were given to this user
> SELECT INTO group_id_count_v count(*) FROM membership
> WHERE user_id = user_id_p;
>
> -- select all that have groups shared by the linked user and
> -- have the right number (or more)
> FOR foo IN SELECT group_set_id FROM group_sets
> WHERE group_id IN
> (SELECT group_id FROM membership
> WHERE user_id = user_id_p)
> GROUP BY group_set_id
>
> HAVING count(*) = group_id_count_v
> LOOP
>
> -- make sure it has only the right number of group_ids
> SELECT INTO count_v count(*) FROM group_sets
> WHERE group_set_id = foo.group_set_id;
>
> IF group_id_count_v = count_v THEN
> RETURN foo.group_set_id;
> END IF;
>
> END LOOP;
>
> RETURN -1;
> END;
> ' LANGUAGE 'plpgsql';
> ----------------------------------------------------------------
>