用左连接完成对一个表中的多个外键字段替换查询返回名称

---------- 创建4个表结构，其中jobs表中的三个字段cityID、provinceID、countryID对应着其他3个表的主键

CREATE TABLE [dbo].[city] (
 [ID] [smallint] IDENTITY (1, 1) NOT NULL ,
 [cityName] [varchar] (50) COLLATE Chinese_PRC_CI_AS NULL
) ON [PRIMARY]
GO

CREATE TABLE [dbo].[country] (
 [ID] [smallint] IDENTITY (1, 1) NOT NULL ,
 [countryName] [varchar] (50) COLLATE Chinese_PRC_CI_AS NULL
) ON [PRIMARY]
GO

CREATE TABLE [dbo].[jobs] (
 [job_id] [smallint] IDENTITY (1, 1) NOT NULL ,
 [userName] [varchar] (50) COLLATE Chinese_PRC_CI_AS NULL ,
 [cityID] [int] NULL ,
 [provinceID] [int] NULL ,
 [countryID] [int] NULL ,
 [productName] [varchar] (50) COLLATE Chinese_PRC_CI_AS NULL
) ON [PRIMARY]
GO

CREATE TABLE [dbo].[province] (
 [ID] [smallint] IDENTITY (1, 1) NOT NULL ,
 [provinceName] [varchar] (50) COLLATE Chinese_PRC_CI_AS NULL
) ON [PRIMARY]
GO

 

----查询jobs表中的三个外键对应的名称

---t1 get countryName
select job_id, userName, provinceID,countryName,ProductName
from jobs as t1 left  join country t2 on t2.id = t1.countryID

-- get countryName and provinceName
select job_id, userName, provinceName,countryName,ProductName
from (
 select job_id, userName, provinceID,countryName,ProductName
 from jobs as t1 left  join country t2 on t2.id = t1.countryID
     ) as t3 left join Province t4 on t3.provinceID = t4.ID

-- get all
select job_id, userName, cityName, provinceName,countryName,ProductName
from(
 select job_id, userName,cityID, provinceName,countryName,ProductName
 from (
  select job_id, userName,cityID, provinceID,countryName,ProductName
  from jobs as t1 left  join country t2 on t2.id = t1.countryID
      ) as t3 left join Province t4 on t3.provinceID = t4.ID
     )  as t5 left join city t6 on t5.cityID = t6.ID