Non-Correlated-iii


#1

Hi, I'm trying to follow the course, had no problem to understand the first sections but suddenly we've jumped to giving tables aliases and stuff without explaining why.

I was doing Section 3 of non-correlated subqueries and I was allowed to pass the section before I'd even properly attempted the query. Can anyone tell me if the below query is correct? I don't want to pass the section without getting it right..

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

The output appears to be correct, but I'm not sure

dep_month	dep_day_of_week	    average_distance
2000-01  	Monday	            1302.0
2000-01 	Saturday	    328.0
2000-01	        Sunday	            691.333333333333

#2

I have problem too. I wrote next quary. And have the same result. But I can pass this exercise.
and have mistake report like "Use select statement to view the table"
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,
distance as flight_distance

      FROM flights
     GROUP BY 1,2,3
   ) a

GROUP BY 1,2
ORDER BY 1,2;


Non correlated iii same issue
#3