How can I create a left join using cross join in SQL?

Question

How can I create a query equivalent to a left join without actually using left join in SQL?

Possible duplicate of [Simulate a left join without using "left join"](https://stackoverflow.com/questions/9159729/simulate-a-left-join-without-using-left-join) — Ankur Sinha, Aug 06 '18 at 09:41
Why would you want to? Do you mean without actually writing "Left join" or that the query plan is without a left join? — Magnus, Aug 06 '18 at 09:44
Your title & body differ. What is your question? What are definitions of left join & cross join that you understand? What are you able to do? Also, this is a faq, so why did other questions not help? — philipxy, Aug 06 '18 at 16:52
Possible duplicate of [LEFT OUTER JOIN EQUIVALENT](https://stackoverflow.com/questions/15572333/left-outer-join-equivalent) — philipxy, Aug 06 '18 at 16:56

score 0 · Answer 1 · answered Aug 06 '18 at 14:11

You can't easily do it with cross join. You can do it with an inner join and union all:

select a.*, b.*
from a join
     b 
     on . . .
union all
select a.*, . . .  -- manually put in b columns
from a
where not exists (select 1 from b where . . . );  -- join conditions in the `where` clause

How can I create a left join using cross join in SQL?

1 Answers1