SQL SELECT and check column from second table - sql

Question

I have two tables in my database. From the Table B i collect some data. I include by using JOIN the data from Table A. In this table there is a column user_id. The user id in table B is the the id from Table A. No i want to get all data from table A but without showing data if the table A id is in the table B column user_id available. I think the trick is the correct usage of JOIN but i need to check the whole column and not just one line.
SQL Query (which is probably not working)
SELECT * FROM tableB
JOIN tableA
ON tableB.user_id = tableA.id
WHERE tableB.user_id != tableA.id
Please see my example i have prepared in Excel:

Answer 1

To select all the data from tableA where id is not available in tableB you don't need join rather you can use not exists or not in.
I would prefer not exists
Using not exists:
SELECT * from tableA a
WHERE NOT EXISTS (
SELECT 1
FROM tableB b
WHERE b.user_id = a.id
);
using not in:
SELECT * from tableA a
WHERE id not in (SELECT user_id FROM tableB );
DB-Fiddle:
create table TableA (id int, name varchar(50), lastname varchar(50));
insert into TableA values(1,'john','smith');
insert into TableA values(2,'Paul','smith');
create table TableB (id int, user_id int, something varchar(50));
insert into TableB values(1,2,'bla');
insert into TableB values(2,3,'bla');
Query: (using not exists)
SELECT * from tableA a
WHERE NOT EXISTS (
SELECT 1
FROM tableB b
WHERE b.user_id = a.id
);
Output:
id
name
lastname
1
john
smith
Query: (using not in)
SELECT * from tableA
WHERE id not in (SELECT user_id FROM tableB );
Output:
id
name
lastname
1
john
smith
db<fiddle here

Answer 2

I think I get what you want. You want not exists:
SELECT *
FROM tableB b JOIN
tableA a
ON b.user_id = a.id
WHERE NOT EXISTS (SELECT 1
FROM tableA a2
WHERE b.user_id = a2.id
);
EDIT:
I wrote the above, but I didn't fully follow the JOIN conditions. You either seem to want to join on id:
SELECT *
FROM tableB b JOIN
tableA a
ON b.id = a.id
WHERE NOT EXISTS (SELECT 1
FROM tableA a2
WHERE b.user_id = a2.id
);
Or no JOIN at all:
SELECT *
FROM tableB b
WHERE NOT EXISTS (SELECT 1
FROM tableA a2
WHERE b.user_id = a2.id
);