# Questions regarding SUBQUERIES III

1. why do we need an “a”?
2. why AS is not used here?
3. why do we put “a.” in the first SELECT?
4. why do we need GROUP BY in inner query? it defines the way you see the output, isn`t it?

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```

SELECT a.dep_month,
a.dep_day_of_week,
AVG(a.flight_distance) AS average_distance
FROM (
SELECT dep_month,
dep_day_of_week,
dep_date,
sum(distance) AS flight_distance
FROM flights
GROUP BY 1,2,3
) a
GROUP BY 1,2
ORDER BY 1,2;

``<do not remove the three backticks above>``

This guy has given a very detailed reply (even too detailed maybe): https://discuss.codecademy.com/t/non-correlated-subqueries-iii-a-few-questions/40537

Then again the code itself looks more complicated than what it could actually be. I get the same results by using:

select dep_month, dep_day_of_week, avg(distance) as average_distance
from flights
group by 1,2
order by 1,2;

I think they chose a question that is not really suited for an inner vs outer query type of excercise…

2 Likes

select r.dep_month,
r.dep_day_of_week,
AVG(r.flight_count) AS average_flights

``````   from (SELECT dep_month,
dep_day_of_week,
dep_date,
COUNT(*) AS flight_count
FROM flights
where dep_day_of_week ='Friday'
GROUP BY 1,2,3) r
GROUP by 1

;
``````

we can choose any name , here i choose r as a temporary table , in the given solution they choose a as a name of this table , but we ask as the AVG of flight per month for every Friday , so we need this condition ( where dep_day_of_week =‘Friday’)
i hope that i give you some explanation

im having the same problem

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