Oracle SQL non-unique table alias in one Select

I'd lay money on "Oracle bug" - Of all the things that've most held me back from adopting the ANSI JOIN syntax, it's been Oracle's painfully egregious and bug-laden implementation thereof. That said, "Failure to catch a syntax error" is pretty minor, and Oracle has, as far as I can tell, largely cleaned up their act.

The first two queries below are equivalent. In the ON clause of the join the table alias x only refers to the last table to use that alias so only the employee table is restricted.

In the SELECT and WHERE expressions the x alias refers to both tables - so, where the column names are unique then they can be successfully referenced but where there are identical column names then oracle raises an ORA-00918: column ambiguously defined exception (as happens in query 3 if the comment is removed).

I can't find any documentation on this but it looks very like a bug.

SQL Fiddle

Oracle 11g R2 Schema Setup:

CREATE TABLE employee (  company_id    NUMBER(3),  employee_name VARCHAR2(20));CREATE TABLE company (  company_id    NUMBER(3),  company_name VARCHAR2(20));INSERT INTO employee VALUES ( 4, 'Four Emp' );INSERT INTO employee VALUES ( 5, 'Five Emp' );INSERT INTO employee VALUES ( 6, 'Six Emp' );INSERT INTO company VALUES ( 4, 'Four Company' );INSERT INTO company VALUES ( 5, 'Five Company' );INSERT INTO company VALUES ( 6, 'Six Company' );

Query 1:

SELECT *FROM   company  x       JOIN       employee x       ON x.company_id = 5

Results:

| COMPANY_ID | COMPANY_NAME | EMPLOYEE_NAME ||------------|--------------|---------------||          5 | Four Company |      Five Emp ||          5 | Five Company |      Five Emp ||          5 |  Six Company |      Five Emp |

Query 2:

SELECT *FROM   company x       CROSS JOIN       (SELECT * FROM employee WHERE company_id = 5) x

Results:

| COMPANY_ID | COMPANY_NAME | EMPLOYEE_NAME ||------------|--------------|---------------||          5 | Four Company |      Five Emp ||          5 | Five Company |      Five Emp ||          5 |  Six Company |      Five Emp |

Query 3:

SELECT --x.company_id,       x.company_name,       x.employee_nameFROM   company x       CROSS JOIN       (SELECT * FROM employee WHERE company_id = 5) x

Results:

| COMPANY_NAME | EMPLOYEE_NAME ||--------------|---------------|| Four Company |      Five Emp || Five Company |      Five Emp ||  Six Company |      Five Emp |