Question

SQL问题：

我有一个包含3列的表格： From_City，To_City，Trip_Count 和4行：

+-----------+---------+------------+
| From_City | To_City | Trip_Count |
+-----------+---------+------------+
| Berlin    | London  |          2 |
| London    | Berlin  |          3 |
| Sydney    | Tokyo   |          4 |
| Tokyo     | Sydney  |          6 |
+-----------+---------+------------+

我想将城市之间的旅行总结为一个只有2行的新表：

+--------+------------+------------+
|  City  | Other_City | Trip_Count |
+--------+------------+------------+
| Berlin | London     |          5 |
| Sydney | Tokyo      |         10 |
+--------+------------+------------+

我无法弄清楚如何在SQL（最好是SQL Server）中实现这一点。有什么建议？谢谢！

注意：两个城市之间的顺序并不重要。无论是柏林 - 伦敦还是伦敦 - 柏林都可以。

Answer 1

试试这个：

SELECT CASE 
           WHEN From_City < To_City THEN From_City 
           ELSE To_City 
       END AS City,
       CASE 
           WHEN From_City >= To_City THEN From_City 
           ELSE To_City 
       END AS Other_City,
       SUM(Trip_Count) AS Trip_Count
FROM mytable
GROUP BY CASE WHEN From_City < To_City THEN From_City ELSE To_City END,
         CASE WHEN From_City >= To_City THEN From_City ELSE To_City END

Answer 2

更新：正如FLICKER指出的那样;这在SQL Server中不起作用，因为SQL Server不能提供LEAST和GREATEST，也不提供SQLite中的MIN / MAX等类似功能。遗憾。

您获得了LEAST的第一个城市和GREATEST的另一个城市：

create table full_trips as ( select least(from_city, to_city) as city, greatest(from_city, to_city) as other_city, sum(trip_count) as trip_count from trips group by least(from_city, to_city), greatest(from_city, to_city) );

跨越行的SQL总和＆＃34;匹配＆＃34;？

2 个答案: