[英]How to use triple INNER JOIN with one empty table?
Given is the following table:给定的是下表:
CREATE TABLE projects
(
project_id integer,
name character varying(50),
owner_user integer NOT NULL,
owner_org integer NOT NULL,
)
A project can be either owned by a user ( user_id
), OR by an organization ( org_id
) So either field is 0. So I do an INNER JOIN on projects
, users
, and organizations
, but if the project is owned by a user (and currently no organization does exist at all), the result is empty.项目可以由用户( user_id
)拥有,也可以由组织( org_id
)拥有,因此任何一个字段都是0。所以我对projects
、 users
和organizations
进行了INNER JOIN,但如果项目归用户所有(并且目前根本不存在任何组织),结果为空。
Does NOT work不工作
SELECT *
FROM users u, projects p, organizations o
WHERE (p.owner_org != 0 AND o.org_id = p.owner_org) OR
(p.owner_user != 0 AND u.user_id = p.owner_user);
Can anyone help me out?谁能帮我吗? If I leave out organization
, the result is 1 row, as expected.如果我省略了organization
,结果是 1 行,正如预期的那样。
Works作品
SELECT *
FROM projects p, users u
WHERE (p.owner_user != 0 AND u.user_id = p.owner_user);
Learn to use proper, explicit, standard , readable JOIN
syntax.学习使用正确的、明确的、标准的、可读的JOIN
语法。
You seem to want:你似乎想要:
select *
from projects p left join
users u
on p.owner_org = o.org_id left join
organizations o
on p.owner_user = u.user_id ;
I assume there is no id of 0
in the projects
or organizations
tables so the filtering is not necessary.我假设projects
或organizations
表中没有0
的 id,因此不需要过滤。
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