给定场景的国家和城市数据的排序查询

Question

我的输入数据如下：

**Country          city**
Australia     Sydney
Australia     melbourne
India         Delhi
India         Chennai
India         Bangalore
Afghanistan   Kabul

预期输出为：

Afghanistan
Kabul
Australia
melbourne
syndey
India
Bangalore
Chennai
Delhi

两列中的数据应按字母顺序排列（城市级别和国家级别），结果应为包含上述值的单列。该国家/地区应按字母顺序排列，相应的城市应在其下方，也应按字母顺序排列。如果不在单个查询中使用中间 table 如何做到这一点？

Answer 1

您需要 UNION ALL 查询才能在结果中针对每个国家/地区获取一行，针对每个城市获取一行：

select coalesce(city, country) as location
from
(
  select distinct country, null as city from mytable
  union all
  select country, city from mytable
)
order by country, city nulls first;

Answer 2

这有一个 table 扫描，也不需要使用 UNION 来获得不同的结果：

SQL Fiddle

Oracle 11g R2 架构设置:

CREATE TABLE cities ( Country, city ) AS
SELECT 'Australia',     'Sydney' FROM DUAL UNION ALL
SELECT 'Australia',     'melbourne' FROM DUAL UNION ALL
SELECT 'India',         'Delhi' FROM DUAL UNION ALL
SELECT 'India',         'Chennai' FROM DUAL UNION ALL
SELECT 'India',         'Bangalore' FROM DUAL UNION ALL
SELECT 'Afghanistan',   'Kabul' FROM DUAL;

查询 1:

SELECT value
FROM   (
  SELECT c.*,
         country AS ctry,
         ROW_NUMBER() OVER ( PARTITION BY Country ORDER BY city ) AS rn
  FROM   cities c
)
UNPIVOT( value FOR key IN ( Country AS 1, City AS 2 ) )
WHERE rn = 1 OR key = 2
ORDER BY ctry, rn, key

Results:

|       VALUE |
|-------------|
| Afghanistan |
|       Kabul |
|   Australia |
|      Sydney |
|   melbourne |
|       India |
|   Bangalore |
|     Chennai |
|       Delhi |

给定场景的国家和城市数据的排序查询

Ordering Query for Country & City data for the scenario given

sql

oracle

sql-order-by