Simplifying a query with correlated subquery to simple joins - sql

Question

I need help in simplifying the below query.
I was able to check for '0' count without using Group By/having Count clauses in the below query but with correlated subquery.
Now, I've been asked to simplify the below query as simple joins!.
I tried merging the query into one. But the output differs.
Could you please suggest any other idea of simplifying the query, which is checking for '0' count.
select distinct tab1.col1
from tab1
where tab1.col2 = 'A'
And 0 = (select count(tab2.col1)
from tab2
where tab2.col2 = 'B'
and tab2.col1 = tab1.col1)

Answer 1

This sort of thing would normally be written as a NOT EXISTS
SELECT distinct tab1.col1
FROM tab1
WHERE tab1.col2 = 'A'
AND NOT EXISTS(
SELECT 1
FROM tab2
WHERE tab2.col2 = 'B'
AND tab2.col1 = tab1.col1 )
However you could also write
SELECT tab1.col1, count(tab2.col1)
FROM (SELECT * FROM tab1 WHERE col2 = 'A') tab1,
(SELECT * FROM tab2 WHERE col2 = 'B') tab2
WHERE tab1.col1 = tab2.col2(+)
GROUP BY tab1.col1
HAVING count(tab2.col1) = 0

Answer 2

Try some of these.
If col1 is declared as not null, the first two queries have the same execution plan (anti-joins). The second alternative is my personal advice, since it matches your requirements the best.
-- Non-correlated subquery
select distinct col1
from tab1
where col2 = 'A'
and col1 not in(select col1
from tab2
where col2 = 'B');
-- Correlated subquery
select distinct col1
from tab1
where col2 = 'A'
and not exists(select 'x'
from tab2
where tab2.col2 = 'B'
and tab2.col1 = tab1.col1);
-- Using join
select distinct tab1.col1
from tab1
left join tab2 on(tab2.col2 = 'B' and tab2.col1 = tab1.col1)
where tab1.col2 = 'A'
and tab2.col1 is null;
-- Using aggregation
select tab1.col1
from tab1
left join tab2 on(tab2.col2 = 'B' and tab2.col1 = tab1.col1)
where tab1.col2 = 'A'
group
by tab1.col1
having count(tab2.col2) = 0;