Getting rows from two tables with a join and where clause - mysql

Question

I am needing to get users from a 'users' table that are not equal to my username, but also not in a blocked table as the 'blockee'.
Using only the users table, I am doing:
SELECT * FROM users WHERE username != <myself> AND interests LIKE <string>;
However, since I've added the additional 'blocked' table, I'm needing to further filter them.
mysql> describe users;
+-----------+--------------+------+-----+---------+----------------+
| Field | Type | Null | Key | Default | Extra |
+-----------+--------------+------+-----+---------+----------------+
| id | int(11) | NO | PRI | NULL | auto_increment |
| username | varchar(255) | NO | | NULL | |
| password | varchar(255) | NO | | NULL | |
| email | varchar(255) | NO | | NULL | |
| city | varchar(60) | NO | | NULL | |
| state | varchar(60) | NO | | NULL | |
| lat | decimal(8,6) | YES | | NULL | |
| lng | decimal(9,6) | YES | | NULL | |
| interests | text | YES | | NULL | |
| hash | varchar(32) | YES | | NULL | |
| active | int(1) | YES | | NULL | |
| avatar | varchar(255) | YES | | NULL | |
+-----------+--------------+------+-----+---------+----------------+
12 rows in set (0.00 sec)
mysql> describe blocked;
+---------+--------------+------+-----+---------+----------------+
| Field | Type | Null | Key | Default | Extra |
+---------+--------------+------+-----+---------+----------------+
| id | int(11) | NO | PRI | NULL | auto_increment |
| blocker | varchar(255) | NO | | NULL | |
| blockee | varchar(255) | NO | | NULL | |
+---------+--------------+------+-----+---------+----------------+
3 rows in set (0.00 sec)
I attempted:
SELECT * FROM users JOIN blocked ON users.username = blocked.blocker WHERE username != 'myself' AND blocked.blockee IS NULL;
A pseudo-query would look like:
"give me every user that's not equal to my username, but is also not a blockee where I am the blocker"
So, if I had these values in the blocked table:
+----+-----------+----------+
| id | blocker | blockee |
+----+-----------+----------+
| 1 | myself | testuser |
+----+-----------+----------+
It would return everyone that is not testuser and had the same values in the interests column as the LIKE clause.
I hope this makes sense. I'm stuck.

Answer 1

This query will give you the list of all users who are not you and are not blocked by you. You can then add other conditions (such as AND interests LIKE <string>) to the WHERE clause as necessary.
SELECT u.*
FROM users u
LEFT JOIN blocked b
ON b.blockee != u.username AND b.blocker = 'myself'
WHERE u.username != 'myself' AND b.blockee IS NOT NULL
Demo on dbfiddle

Answer 2

Here's the query that will do what you're looking for:
select *
from users u
where u.username != 'myself'
and not exists (
select 1
from blocked b
where b.blocker = 'myself'
and b.blockee = u.username
)
and u.interests like '%what%';
I put together an example you can execute to see how it behaves: https://rextester.com/GPEC60793
Here's a copy of the entire demo:
drop table if exists demo_users;
drop table if exists demo_blocked;
create table demo_users (id int auto_increment, username varchar(255), interests text, primary key (id));
create table demo_blocked (id int auto_increment, blocker varchar(255), blockee varchar(255), primary key (id));
insert into demo_users (username, interests)
values ('myself', 'whatever'),
('testuser', 'blah'),
('somebody', 'foo'),
('nobody', 'whatfor');
insert into demo_blocked (blocker, blockee)
values ('myself', 'testuser');
select * from demo_users;
select * from demo_blocked;
select *
from demo_users u
where u.username != 'myself'
and not exists (
select 1
from demo_blocked b
where b.blocker = 'myself'
and b.blockee = u.username
)
and u.interests like '%what%';
drop table demo_users;
drop table demo_blocked;

Answer 3

If you don't care about performance, you can try sub query.
SELECT * FROM users WHERE username != 'myself' and user.username not in (select locker from blocked);
I think it will work correctly for you

Answer 4

This should work - but again I don't have your test data to test it against.
Cheers
SELECT *
FROM users
WHERE ( 1 = 1 )
AND ( username ! = 'myself OR username not in ( select username from blocked ))
AND interests like '%string%';
in the predicate yo may need to change the OR to an AND - as I said no data to test my logic.
HTH!

Answer 5

First get a list of your blockee, then try to match those with your user table, if you cant find a match you will have null blockee, and those are the users you want.
SELECT u.*
FROM users u
LEFT JOIN ( SELECT b.blockee
FROM blocked b
WHERE b.blocker = 'myself') as b
ON o.username = b.blockee
WHERE b.blockee IS NULL
AND u.interests LIKE <string>
AND u.username != 'myself' -- if blocker cant be the same as blockee
-- you dont need this one