亲子关系到平面视图

Question

是否有一种简单的方法可以将具有父子关系的表迁移到第一列？

INPUT_TABLE

PARENT_ID,ID,NAME
null,1, USA
1   ,2, Las Vegas
2   ,3, City in las Vegas
2   ,4, Another City in las Vegas
.. a lot more

输出

ID, COUNTRY, CITY, PLACE
1,  USA, null,null
2,  USA, Las Vegas,null
3,  USA, Las Vegas,City in las Vegas
4,  USA, Las Vegas,Another City in las Vegas

提前致谢

Answer 1

根据您的评论，如果你有3个项目的层级，并且不需要保留没有City或Place的行，那么将表连接两次就足够了。

SQL语句

SELECT  ID = Country.ID
        , Country = Country.NAME
        , City = City.NAME
        , Place = Place.Name
FROM    q Country
        INNER JOIN q City ON City.PARENT_ID = Country.ID
        INNER JOIN q Place ON Place.PARENT_ID = City.ID

（SQL Server）测试脚本

;WITH q (PARENT_ID, ID, NAME) AS (
  SELECT null, 1, 'USA'
  UNION ALL SELECT 1, 2, 'Las Vegas'
  UNION ALL SELECT 2, 3, 'City in las Vegas'
  UNION ALL SELECT 2, 4, 'Another City in las Vegas'
)
SELECT  ID = Country.ID
        , Country = Country.NAME
        , City = City.NAME
        , Place = Place.Name
FROM    q Country
        INNER JOIN q City ON City.PARENT_ID = Country.ID
        INNER JOIN q Place ON Place.PARENT_ID = City.ID