Oracle group by Alias - sql

Question

Orale is returning an error in the group by using alias column.
SELECT
CONCAT( CONCAT( a.air_location, ' ,' ), a.air_code ) AS "Departs From",
CONCAT( CONCAT( ad.air_location, ' ,' ), ad.air_code ) AS "Arrives At",
MIN(f.fl_fare) AS "Minimun Fare"
FROM flight f
INNER JOIN airport a ON a.air_code = f.fl_dest
INNER JOIN airport ad ON ad.air_code = f.fl_orig
GROUP BY "Departs From", "Arrives At";
It is returning:
ORA-00904: "Arrives At": invalid identifier
00904. 00000 - "%s: invalid identifier"
*Cause:
*Action:
Error at Line: 10 Column: 26

Answer 1

You can't use a column alias in the GROUP BY clause in Oracle - and positional parameters are not supported either. You need to repeat the expression, or use a subquery or cte. So:
select
ao.air_location || ' ,' || ao.air_code as departs_from,
ad.air_location || ' ,' || ad.air_code as arrives_at,
min(f.fl_fare) as minimun_fare
from flight f
inner join airport ad on ad.air_code = f.fl_dest
inner join airport ao on ao.air_code = f.fl_orig
group by
ao.air_location || ' ,' || ao.air_code
ad.air_location || ' ,' || ad.air_code
Other changes to your query:
changed table aliases to names that seem more meaningful to me (and I think you had the origin and destination inverted in the result)
used standard ANSI string concatenation operator || instead of CONCAT(), which Oracle supports
used column aliases that do not require quoting (without embedded spaces), because it makes the query easier to write - you can revert that change if you really want otherwise.
As a final thought: here is an alternative that uses a lateral join to generate the aliases:
select x.departs_from, x.arrives_at, min(f.fl_fare) as minimun_fare
from flight f
inner join airport ad on ad.air_code = f.fl_dest
inner join airport ao on ao.air_code = f.fl_orig
cross apply (
select
ao.air_location || ' ,' || ao.air_code as departs_from,
ad.air_location || ' ,' || ad.air_code as arrives_at
from dual
) x
group by x.departs_from, x.arrives_at

Answer 2

Wrap your CONCAT query up in a derived table, GROUP BY its result:
SELECT "Departs From", "Arrives At", MIN(fl_fare) as minimun_fare
FROM
(
SELECT
CONCAT( CONCAT( a.air_location, ' ,' ), a.air_code ) AS "Departs From",
CONCAT( CONCAT( ad.air_location, ' ,' ), ad.air_code ) AS "Arrives At",
f.fl_fare
FROM flight f
INNER JOIN airport a ON a.air_code = f.fl_dest
INNER JOIN airport ad ON ad.air_code = f.fl_orig
) dt
GROUP BY "Departs From", "Arrives At";
(The GROUP BY is evaluated before the SELECT list. So the column aliases can't be used in the GROUP BY since they don't yet exist.)