Postgresql query results to depend on few rows of same table - postgresql

Question

I'm working on some application, and we're using postgres as our DB. I don't a lot of experience with SQL at all, and now i encountered a problem, that i can't find answer to.
So here's a problem:
We have privacy settings stored in separate table, and accessibility of each row of data depends on few rows of this privacy table.
Basically structure of privacy table is:
entityId | entityType | privacyId | privacyType | allow | deletedAt
-------------------------------------------------------------------
5 | user | 6 | user | f | //example entry
5 | user | 1 | user_all | t |
In two words, this settings mean, that user id5 allows to have access to his data to everybody except user id6.
So i get available data by query like:
SELECT <some_relevant_fields> FROM <table>
JOIN <join>
WHERE
(privacy."privacyId"=6 AND privacy."privacyType"='user' AND privacy.allow=true)
OR (
(privacy."privacyType"='user_all' AND privacy."deletedAt" IS NOT NULL)
AND
(privacy."privacyType"='user' AND privacy."privacyId"=6 AND privacy.allow!=false)
);
I know that this query is incorrect in this form, but i want you to get idea of what i try to achieve.
So it must check for field with its type/id and allow=true, OR check that user_all is not deleted(deletedAt field is null) and there is no field restricting access with allow=false to this user.
But it seems like postgres is chaining all expressions, so it overrides privacy."privacyType"='user_all' with 'user' at the end of expression, and returns no results, or returns data even if user "blocked", because 'user_all' exist.
Is there a way to write WHERE clause to return result if AND expression is true for 2 different rows, for example in code above: (privacy."privacyType"='user_all' AND privacy."deletedAt" IS NOT NULL) is true for one row AND (privacy."privacyType"='user' AND privacy."privacyId"=6 AND privacy.allow!=false) is true for other, or maybe check for absence of row with this values.

Answer 1

Is this what you want?
select <some_fields> from <table> where
privacyType='user_all' AND deletedAt IS NOT NULL
union
select <some_fields> from <table> where
privacyType='user' AND privacyId=6 AND allow<>'f';

Answer 2

You left join the table with itself and found what element doesnt have a match using the where.
SELECT p1.*
FROM privacy p1
LEFT JOIN privacy p2
ON p1."entityId" = p2."entityId"
AND p1."privacyType" = 'user_all'
AND p1."deletedAt" IS NULL
AND p2."privacyType"='user' AND
AND p2."privacyId"= 6
AND p2.allow!=false
WHERE
p2.privacyId IS NOT NULL