2112. The Airport With the Most Traffic

SQL架构

Table: Flights

+-------------------+------+
| Column Name       | Type |
+-------------------+------+
| departure_airport | int  |
| arrival_airport   | int  |
| flights_count     | int  |
+-------------------+------+
(departure_airport, arrival_airport) is the primary key column for this table.
Each row of this table indicates that there were flights_count flights that departed from departure_airport and arrived at arrival_airport.

Write an SQL query to report the ID of the airport with the most traffic. The airport with the most traffic is the airport that has the largest total number of flights that either departed from or arrived at the airport. If there is more than one airport with the most traffic, report them all.

Return the result table in any order.

The query result format is in the following example.

Example 1:

Input: 
Flights table:
+-------------------+-----------------+---------------+
| departure_airport | arrival_airport | flights_count |
+-------------------+-----------------+---------------+
| 1                 | 2               | 4             |
| 2                 | 1               | 5             |
| 2                 | 4               | 5             |
+-------------------+-----------------+---------------+
Output: 
+------------+
| airport_id |
+------------+
| 2          |
+------------+
Explanation: 
Airport 1 was engaged with 9 flights (4 departures, 5 arrivals).
Airport 2 was engaged with 14 flights (10 departures, 4 arrivals).
Airport 4 was engaged with 5 flights (5 arrivals).
The airport with the most traffic is airport 2.

Example 2:

Input: 
Flights table:
+-------------------+-----------------+---------------+
| departure_airport | arrival_airport | flights_count |
+-------------------+-----------------+---------------+
| 1                 | 2               | 4             |
| 2                 | 1               | 5             |
| 3                 | 4               | 5             |
| 4                 | 3               | 4             |
| 5                 | 6               | 7             |
+-------------------+-----------------+---------------+
Output: 
+------------+
| airport_id |
+------------+
| 1          |
| 2          |
| 3          |
| 4          |
+------------+
Explanation: 
Airport 1 was engaged with 9 flights (4 departures, 5 arrivals).
Airport 2 was engaged with 9 flights (5 departures, 4 arrivals).
Airport 3 was engaged with 9 flights (5 departures, 4 arrivals).
Airport 4 was engaged with 9 flights (4 departures, 5 arrivals).
Airport 5 was engaged with 7 flights (7 departures).
Airport 6 was engaged with 7 flights (7 arrivals).
The airports with the most traffic are airports 1, 2, 3, and 4.

with t1 as (
select
airport_id,sum(flights_count) flights_count   #每个机场的总航班数
from
(
select
departure_airport airport_id,flights_count 
from
Flights
 
union all
 
select
arrival_airport airport_id,flights_count
from
Flights
)s1
group by 
airport_id
)
select
airport_id
from
(
select
airport_id,dense_rank() over( order by flights_count desc) dr #按航班数标号(同数同号)
from
t1
) s2
where dr = 1 #选出标号为1的就是题中需求