Querying across multiple tables avoiding a union all - sql

Question

I have the following DB tables that I am trying to query:
t_shared_users
user_id
user_category
folder_id
expiry
t_documents
id
folder_id
user_id
user_category
description
created
updated
t_folder
id
type
user_id
user_category
created
updated
I would like to find all the documents you own and have shared access to. ie. search for all documents in t_documents where user_id = 1 AND user_category = 100 but also include those documents in the folder you have access to in t_shared_users. Here is my attempt at the query:
SELECT
id,
folder_id,
user_id,
user_category,
description,
created,
updated
FROM
t_documents
WHERE
user_category = 100
AND user_id = 1
UNION ALL
SELECT
d.id,
d.folder_id,
d.user_id,
d.user_category,
d.description,
d.created,
d.updated
FROM
t_documents d
JOIN
t_shared_users s
ON
d.folder_id = s.folder_id
WHERE
d.user_category = 100
d.AND user_id = 1
ORDER BY
created ASC
LIMIT
10
Is there any better/more performant/concise way to write this query? The above seems a little verbose and slow.
edit:
CREATE TABLE t_folder (
id SERIAL NOT NULL,
user_category SMALLINT NOT NULL,
user_id INTEGER NOT NULL,
type INTEGER NOT NULL,
description TEXT,
created TIMESTAMP WITH TIME ZONE NOT NULL DEFAULT now(),
updated TIMESTAMP WITH TIME ZONE NOT NULL DEFAULT now(),
PRIMARY KEY (id)
);
CREATE TABLE t_documents (
id BIGSERIAL NOT NULL,
folder_id INTEGER,
user_category SMALLINT NOT NULL,
user_id INTEGER NOT NULL,
description TEXT NOT NULL,
created TIMESTAMP WITH TIME ZONE NOT NULL DEFAULT now(),
updated TIMESTAMP WITH TIME ZONE NOT NULL DEFAULT now(),
PRIMARY KEY (id)
);
CREATE TABLE t_shared_users (
id SERIAL,
folder_id INTEGER NOT NULL,
user_category INTEGER NOT NULL,
user_id INTEGER NOT NULL,
expiry TIMESTAMP WITH TIME ZONE NOT NULL DEFAULT now(),
PRIMARY KEY (id)
);

Answer 1

This is your query:
SELECT
id,
folder_id,
user_id,
user_category,
description,
created,
updated
FROM
t_documents
WHERE
user_category = 100
AND user_id = 1
UNION ALL
SELECT
d.id,
d.folder_id,
d.user_id,
d.user_category,
d.description,
d.created,
d.updated
FROM
t_documents d
JOIN
t_shared_users s
ON
d.folder_id = s.folder_id
WHERE
d.user_category = 100
AND d.user_id = 1 -- your query actually has a typo here
What I don't understand about the above query is why you are filtering on d.user_category and d.user_id (t_documents table) in the bottom part of the query. Are you sure you didn't mean s.user_category and s.user_id (t_shared_users)? If not, what is the point of joining with t_shared_users?
Assuming that I am correct that your query is in error, this is how I would rewrite it:
select d.*
from t_documents d
where d.user_category = 100
and d.user_id = 1
union
select d.*
from t_shared_users s
join t_documents d
on d.folder_id = s.folder_id
where s.user_category = 100
and s.user_id = 1
Notice that I use union instead of union all, as I believe it's technically possible to get possibly unwanted duplicate documents otherwise.
Also, just as a rough approximation, these are the indexes I would define for good performance:
t_documents (user_id, user_category)
t_documents (folder_id)
t_shared_users (user_id, user_category, folder_id)

Answer 2

Starting from the query, you have given, I would replace join with left join
select
d.id,
d.folder_id,
d.user_id,
d.user_category,
d.description,
d.created,
d.updated
from t_documents d
left join t_shared_users s on d.folder_id = s.folder_id
where (d.user_category = 100 and d.user_id = 1)
or (s.user_category = 100 and s.user_id = 1)
This would give you all entries from t_documents with user_id = 1 and user_category = 100, and also all entries with the same where clause, where you have access to shared documents.