My conclusion is that(Tested on 12c):
thus :
SELECT {T / t} FROM (SELECT 1 AS T FROM DUAL); -- Correct
SELECT "tEST" FROM (SELECT 1 AS "tEST" FROM DUAL); -- Correct
SELECT {"TEST" / tEST} FROM (SELECT 1 AS "tEST" FROM DUAL ); -- Incorrect
SELECT test_value AS "doggy" FROM test ORDER BY "doggy"; --Correct
SELECT test_value AS "doggy" FROM test WHERE "doggy" IS NOT NULL; --You can not do this, column alias not supported in WHERE & HAVING
SELECT * FROM test "doggy" WHERE "doggy".test_value IS NOT NULL; -- Do not use AS preceding table alias
So, the reason why USING AS AND "" causes problem is NOT AS
Note: "" double quotes are required if alias contains space OR if it contains lower-case characters and MUST show-up in Result set as lower-case chars. In all other scenarios its OPTIONAL and can be ignored.