Question

我有以下表格结构：

发货（将IDDestination作为外键） - ＆gt;目的地（将IDCity作为外键） - ＆gt; City（将IDCountry作为外键）。

我想为我的存储过程提供一个国家/地区ID，并让它返回所有货件。我如何使用纯SQL语法执行此操作？我可以用ORM来做这件事，但我强迫自己学习这个。

Answer 1

对于visual demonstration of various JOINs, see this link。

假设@idcountry是整数数据类型，请使用：

SET ANSI_NULLS ON
GO
SET QUOTED_IDENTIFIER ON
GO

CREATE PROCEDURE get_shipments_for_countryid 
   @idcountry INT
AS
BEGIN

   SELECT DISTINCT 
          s.*
     FROM SHIPMENT s
     JOIN DESTINATION d ON d.id = s.iddestination
     JOIN CITY c ON c.id = d.idcity 
    WHERE c.idcountry = @idcountry
END
GO

将参数数据类型（如果不是INT）更改为适当的值。

如果任何表格是多对多或一对多的话，DISTINCT是必要的......

Answer 2

SELECT s.*
FROM City c INNER JOIN (
  Shipment s INNER JOIN Destination d ON s.IDDestination = d.ID)
  ON c.ID = d.IDCity
WHERE c.IDCountry = @IDCountry

Answer 3

您可以使用INNER JOIN将所有表链接在一起。

CREATE GetShipments

@CountryID int

AS

SELECT *
FROM Shipments
INNER JOIN Destination ON Shipment.IDDestination = Destination.ID
INNER JOIN Cities ON Destination.IDCity = Cities.ID
WHERE Cities.IDCountry = @CountryID

Answer 4

像这样......也可能......

select * from Shipment as s
inner join Destination as d on s.IDDestination = d.IDDestination
inner join City as c on d.IDCountry = c.IDCountry
where c.IDCountry = @CountryID

Answer 5

SELECT S.* 
FROM Shipment S
JOIN Destination D on S.IDDestination  = D.ID
JOIN City C on D.IDCity = C.ID
WHERE IDCountry = @IDCountry

使用几个外键帮助SQL查询

5 个答案: