Question

我的表格结构如下，样本数据如下姓名：用户

User   Region
Sam    USA    
Meyer  NA    
Ying   Japan    
Yang   Asia

我还有另一张表，包括地区和国家

名称：地区

       Region Country         RegionList    
        USA     America            
        NA       NULL          USA            
        NA      Canada            
        NA      Mexico            
        Japan   Japan
        Asia     NULL         Central        
        Asia      NULL         East        
        Central  India        
        East     Dubai
        Central  Japan

如何编写SQL服务器查询以列出他/她所代表的每个用户及相应的国家/地区？

像：

Sam   America
Meyer America
Meyer Canda
Meyer Mexico
Ying  Japan
Yang  Japan
Yang  India
Yang  Dubai

Answer 1

如果您的Region表可能无限多级，您可以使用Common Table Expression。见Recursive Queries Using Common Table Expressions.

WITH UserRegions (username, region, country)
AS
(
    -- Anchor member definition
    SELECT u.[user] AS username, r.regionlist AS region, r.country
    FROM [User] u
    JOIN Region r
        ON u.Region = r.Region
    UNION ALL
    -- Recursive member definition
    SELECT ur.username, r.regionlist AS region, r.country
    FROM Region r
    INNER JOIN UserRegions AS ur
        ON r.Region = ur.Region
)
-- Statement that executes the CTE
SELECT username, country
FROM UserRegions
WHERE country IS NOT NULL
ORDER BY username

http://sqlfiddle.com/#!3/ca9de/8

Answer 2

您可以使用JOIN获得所需的结果

SELECT user, isNull(Country,RegionList) Country
FROM user
    JOIN region ON users.region = region.region
ORDER BY user, Country

如果您想要返回所有用户，即使他们没有任何国家/地区，那么您可以使用LEFT OUTER JOIN

SELECT user, isNull(isNull(Country,RegionList),'No countries') Country
FROM user
    LEFT OUTER JOIN region ON users.region = region.region
ORDER BY user, Country

Answer 3

根据您提供的显式架构和示例数据：

select
user, isnull(region.country, r2.country) as Country 
from 
user
left join 
region 
on user.region = region.region
left join
region r2
on r2.region = region.regionlist

在多个表中递归的SQL Server查询

3 个答案: