How to perform FULL OUTER JOIN in ORACLE using '+' operator?

Question

Instead of using keywords like FULL OUTER JOIN or FULL JOIN, how can I perform full outer join using \'where\' clause with the help of \'+\' operator?!

Answer 1

Here's an example you can run in oracle to see the results for yourself as well.

with 
a as 
   (select 'A' tbl, level id from dual connect by level < 1000),
b as 
   (select 'B' tbl, level + 500 id from dual connect by level < 1000)
select a.tbl, a.id, b.tbl, b.id from a, b where a.id = b.id(+)
union all
select a.tbl, a.id, b.tbl, b.id from a, b where a.id(+) = b.id and a.id is null

Is the same as:

with 
a as 
   (select 'A' tbl, level id from dual connect by level < 1000),
b as 
   (select 'B' tbl, level + 500 id from dual connect by level < 1000)
select a.tbl, a.id, b.tbl, b.id from a full outer join b on a.id = b.id

Answer 2

You can't (at least directly). Oracle only supports a full outer join using SQL:1999 syntax.

You can fake it by unioning two outer joins:

select a.field1, b.field2
from table_a a, table_b b
where a.id = b.id(+)
union all 
select a.field1, b.field2
from table_a a, table b b
where a.id(+) = b.id
      and a.id is null

It's a lot more readable using the SQL:1999 syntax:

select a.field1, b.field2
from table_a a full outer join table_b b
on a.id = b.id