EXISTS子查询Oracle 11.2与Oracle 12.1

Question

I'm struggling with this weird thing (don't bother about the signification of this exemple, it's just a sample to highlight the issue). The following code runs well on Oracle 12.1.0.2.0, but fails on 11.2.0.3.0.

create table test_0 as
select 1 as un, 2 as deux
from dual
;

create table test_1 as
select 1 as un, 3 as trois
from dual
;             

select deux
from test_0 t0
where exists (select 1 from (select trois from test_1  t1 where t1.un = 
t0.un))
;

Does anyone have an explanation for this?

Answer 1

You are getting this with Oracle before Oracle 12.1

ORA-00904: "T0"."UN": invalid identifier

Because in prior versions, Oracle was not able to determine the context where t0 was defined. So this appears to be an improvement of the version.

Answer 2

"t0.un" (at the very end of your query) is too deeply nested (2 levels, that is). It "works" if you move it level up (disregard the fact that it is probably meaningless) such as

SELECT deux
  FROM test_0 t0
 WHERE EXISTS
          (SELECT trois
                     FROM test_1 t1
                    WHERE t1.un = t0.un);