Question

我有自己加入表。该表用于加入最多4级，即。

Region -> Country -> County -> Town

如何获得Town家长的父母。要执行此操作最多两级，这是查询

SELECT t.ShortName AS Town,
       (SELECT c.ShortName FROM Locations c 
               WHERE c.LocationId = t.ParentId) AS County
FROM Locations t
WHERE t.LocationId = 100

现在想要获得郡的父母国家。

Answer 1

硬编码另一个连接或使用递归CTE。

;with locs as
(
select 1 as level, ShortName, ParentId
from Locations 
WHERE LocationId = 100
UNION ALL
SELECT level + 1, l.ShortName, l.ParentId
FROM Locations l 
JOIN locs ON locs.ParentId = l.LocationId
)
SELECT * FROM locs;

Answer 2

使用名称很好的别名假装它的4个独立的表：

SELECT town.ShortName as TownName,
       county.ShortName as CountyName,
       country.ShortName as CountryName,
       region.ShortName as RegionName
FROM Locations town
INNER JOIN Locations county  ON town.ParentID = county.LocationID
INNER JOIN Locations country ON county.ParentID = country.LocationID
INNER JOIN Locations region  ON country.ParentID = region.LocationID
WHERE town.LocationID = 100

如果不是每个城镇都有县，国家和地区，那么其中一些可能需要LEFT OUTER加入。

在自我加入表中获取父级的父级

2 个答案: