INNER JOIN + LEFT JOIN (Double filtering) - mysql

Question

I'm trying to filter my table where a user has a row in one table, and does not have a row in another. Here's my table structure:
Here's an SQL Fiddle instead: http://sqlfiddle.com/#!9/6e27ed/2
CREATE TABLE users (
user_id INT(11) AUTO_INCREMENT,
name VARCHAR(25),
PRIMARY KEY(user_id)
);
CREATE TABLE photos (
photo_id INT(11) AUTO_INCREMENT,
user_id INT(11) NOT NULL,
PRIMARY KEY(photo_id)
);
CREATE TABLE blocked (
user_id INT(11) NOT NULL,
blocked_id INT(11) NOT NULL
);
INSERT INTO users (name)
VALUES ('returned'), ('not returned'), ('not returned'), ('not returned');
INSERT INTO photos (user_id)
VALUES (1), (2);
INSERT INTO blocked (user_id, blocked_id)
VALUES (4, 2);
Here's the query that I'm trying:
SELECT u.*, min(p.photo_id)
FROM users u
INNER JOIN photos p using(user_id)
LEFT JOIN blocked b ON b.user_id = 4 AND b.blocked_id = u.user_id
WHERE u.user_id != 4
GROUP BY u.user_id
LIMIT 9;
The example data makes it very obvious what the results should be, as the "name" field is filled with "returned", "not returned" in this example, user-id 2 is still returned, but he should be removed by the LEFT JOIN, as user-id 4 has user-id 2 in the blocked-id field of the blocked table.
Expected results from table:
+---------+----------+-----------------+
| user_id | name | min(p.photo_id) |
+---------+----------+-----------------+
| 1 | returned | 1 |
+---------+----------+-----------------+
Received results from query:
+---------+--------------+-----------------+
| user_id | name | min(p.photo_id) |
+---------+--------------+-----------------+
| 1 | returned | 1 |
| 2 | not returned | 2 |
+---------+--------------+-----------------+

Answer 1

It is hard to answer this as I see you are comparing blocked_id=user_id, though in blocked table you also have a user_id column. Only you will know that.
But consider the following
SELECT u.*, min(p.photo_id),b.*
FROM users u
INNER JOIN photos p using(user_id)
LEFT JOIN blocked b ON b.user_id = 4 AND b.blocked_id = u.user_id
WHERE u.user_id != 4 and b.user_id is null
GROUP BY u.user_id
LIMIT 9;
+---------+----------+-----------------+---------+------------+
| user_id | name | min(p.photo_id) | user_id | blocked_id |
+---------+----------+-----------------+---------+------------+
| 1 | returned | 1 | NULL | NULL |
+---------+----------+-----------------+---------+------------+
It turns on the sonar by revealing the b.* columns added as columns 4 and 5. And messes with the where clause a bit.
Edit:
Cleaned up for production
SELECT u.*, min(p.photo_id)
FROM users u
INNER JOIN photos p using(user_id)
LEFT JOIN blocked b ON b.user_id = 4 AND b.blocked_id = u.user_id
WHERE u.user_id != 4 and b.user_id is null
GROUP BY u.user_id
LIMIT 9;

Answer 2

I think you want WHERE b.blocked_id IS NULL to return users that have NOT been blocked by user 4

Answer 3

You can try this one..
SELECT u.*, min(p.photo_id)
FROM users u
INNER JOIN photos p using(user_id)
LEFT JOIN blocked b ON b.blocked_id = u.user_id
GROUP BY u.user_id having min(p.photo_id)<=all(select min(p.photo_id) FROM users u
INNER JOIN photos p using(user_id)
LEFT JOIN blocked b ON b.blocked_id = u.user_id
GROUP BY u.user_id)
;