Anti Join based on multiple keys / columns (SQL) - sql

Question

The setting is simple, I wanted to retrieve all rows from table A that were not present in table B. Because a unique row can be identified using 4 columns, I needed to have a way to write the WHERE statement that it works correctly.
My solution is to concatenate the 4 columns and use that as "one" column/key to do the outer join:
select *
from table_A
where filter_condition = 0
and (column1 || column2 || column3 || column4) not in (
select A.column1 || A.column2 || A.column3 || A.column4
from table_A A -- 1618727
inner join table_B B
on A.column1 = B.column1
and A.column2 = B.column2
and A.column3 = B.column3
and A.column4 = B.column4
and filter_condition = 0
)
My question is, is this a good way of doing this or am I doing something fundamentally wrong?
To be clear, the desired result is simply to get back only the rows of table_A that I "lose" due to the INNER JOIN with table_A and table_B.

Answer 1

You seem to be looking for not exists:
select a.*
from table_a a
where a.filter_condition = 0
and not exists (
select 1
from table_b b
where
a.column1 = b.column1
and a.column2 = b.column2
and a.column3 = b.column3
and a.column4 = b.column4
)
This will give you all records in table_a that do not have a corresponding record in table_b.

Answer 2

Using a LEFT JOIN between A and B and checking for a NULL row in B is probably easier:
SELECT *
FROM table_A A
LEFT JOIN table_B B ON A.column1 = B.column1
AND A.column2 = B.column2
AND A.column3 = B.column3
AND A.column4 = B.column4
WHERE B.column1 IS NULL
AND A.filter_condition = 0

Answer 3

You should be able to use tuples (aka row constructors) in PostgreSQL:
select *
from table_a
where filter_condition = 0
and (column1, column2, column3, column4) not in
(
select column1, column2, column3, column4
from table_b
);
If the columns can be null, then better use NOT EXISTS, as null=null results in "unknown" rather than in true or false.