Simple SQL Question: How to reference an alias identifier in a subquery?

Question

SELECT (subquery, function, or expression) alias,
(SELECT ... FROM tab2 WHERE col=alias)
FROM tab1 WHERE ...
How to do this in Oracle (referencing alias in a subquery)? Thanks.

Answer 1

drop table tab1;
create table tab1(col varchar2(30));
insert into tab1 values('a');
insert into tab1 values('b');
insert into tab1 values('c');
insert into tab1 values('a');
commit;
drop table tab2;
create table tab2 (col varchar2(30));
insert into tab2 values('a');
insert into tab2 values('b');
commit;
SELECT t1.*,
       (SELECT col
          FROM tab2 t2
         WHERE t2.col = t1.alias) AS scalar_t2_col
  FROM (SELECT col,
               LOWER (UPPER (col)) AS alias
          FROM tab1) t1;Or analogously...
WITH  t1 AS (
SELECT col,
       lower(upper(col)) AS alias
  FROM tab1)
SELECT t1.*,
       (SELECT col
          FROM tab2  t2
         WHERE t2.col = t1.alias) AS scalar_t2_col
  FROM t1;