SQL：在 Sql Server 中的连接中需要帮助

Question

我有以下表格，架构是

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表：成员

Id        // PK Int Auto Increment
MemberID
MembershipType        // Holds MemberShipMaster types 1/2/3 for Prem, Corp or Free
RegisteredCountry     // FK of CountryMaster table
RegisteredState       // FK of States Table
RegisteredCity        // FK of Districts table
PostalCountry         // FK of CountryMaster table
PostalState           // FK of States Table
PostalCity            // FK of Districts table

请注意：邮政地址和注册地址可能不同（其逻辑...）

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表：CountryMaster

Id        // PK , int auto increment
Country   // Name of Country

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表：MemberShipMaster

Id               // PK int auto increment
Type             // Type Id int   , 1,2,3 respectively for Prem, Corp and Free
TypeName          // Membership Type Name e.g. Premium, Corporate, Free

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Tbale : 城市

Id,         // PK int auto increment
Name       
StateId     // FK, PK of states table

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表格：状态

Id   // PK int auto increment
Name           
CountryId // FK , PK of COuntry

以下是我的查询

SELECT Id , MemberID, MembershipType, Districts.Name as RegisteredCity,
States.Name as RegisteredState,CountryMaster.Country as RegisteredCountry,
Districts.Name as PostalCity,States.Name as PostalState, CountryMaster.Country as PostalCountry 
FROM   dbo.JFPMembers RIGHT  JOIN MemberShipMaster ON MemberShipMaster.Id= dbo.JFPMembers.MembershipType  
LEFT  JOIN  Districts ON dbo.JFPMembers.PostalCity = Districts.Id OR  Districts.Id =JFPMembers.RegisteredCity
LEFT  JOIN  States ON States.Id = dbo.JFPMembers.RegisteredState OR States.Id = dbo.JFPMembers.PostalState
LEFT  JOIN CountryMaster ON CountryMaster.Id = dbo.JFPMembers.RegisteredCountry and CountryMaster.Id = dbo.JFPMembers.postalCountry
Where Id= @id

我的预期输出：

根据列中保存的 id，在下面的字段中填写适当的城市、州或国家/地区名称。但相反，我在所需的列中得到空值。我已经确认这两个值存在于数据库中以用于连接。

Districts.Name 作为 RegisteredCity，States.Name 作为 RegisteredState，CountryMaster.Country 作为 RegisteredCountry，Districts.Name 作为 PostalCity，States.Name 作为 PostalState，CountryMaster.Country 作为 PostalCountry

Answer 1

你的问题是你试图加入两个不同的条件。而是加入您的查找表两次。像这样：

SELECT Id , MemberID, MembershipType, RegDistricts.Name as RegisteredCity,
    RegStates.Name as RegisteredState, RegCountryMaster.Country as RegisteredCountry,
    PostalDistricts.Name as PostalCity, PostalStates.Name as PostalState, 
    PostalCountryMaster.Country as PostalCountry 
FROM dbo.JFPMembers 
LEFT JOIN MemberShipMaster 
    ON MemberShipMaster.Id = dbo.JFPMembers.MembershipType  
LEFT JOIN Districts RegDistricts
    ON RegDistricts.Id = JFPMembers.RegisteredCity
LEFT JOIN Districts  PostalDistricts
    ON dbo.JFPMembers.PostalCity = PostalDistricts.Id 
LEFT JOIN States RegStates
    ON RegStates.Id = dbo.JFPMembers.RegisteredState 
LEFT JOIN States PostalStates
    ON PostalStates.Id = dbo.JFPMembers.PostalState
LEFT JOIN CountryMaster RegCountryMaster
    ON RegCountryMaster.Id = dbo.JFPMembers.RegisteredCountry 
LEFT JOIN CountryMaster PostalCountryMaster
    ON PostalCountryMaster.Id = dbo.JFPMembers.postalCountry
Where Id= @id

Answer 2

邮政需要通过单独的别名自行连接到各自的国家、州和城市表...与已注册...相同...

SELECT 
      M.Id, 
      M.MemberID, 
      M.MembershipType, 
      MM.TypeName as MembershipTypeName,
      RegCountryAlias.Country as RegisteredCountry,
      RegStatesAlias.Name as RegisteredState,
      RegCitiesAlias.Name as RegisteredCity,
      PostalCountryAlias.Country as PostalCountry,
      PostalStatesAlias.Name as PostalState,
      PostalCitiesAlias.Name as PostalCity
   FROM   
      JFPMembers M
         JOIN MemberShipMaster MM
            ON M.MembershipType = MemberShipMaster.Id

         JOIN CountryMaster as RegCountryAlias
            ON M.RegisteredCountry = RegCountryAlias.ID
         JOIN States as RegStatesAlias
            ON M.RegisteredState = RegStatesAlias.ID
         JOIN Cities as RegCitiesAlias
            ON M.RegisteredCity = RegCitiesAlias.ID

         JOIN CountryMaster as PostalCountryAlias
            ON M.PostalCountry = PostalCountryAlias.ID
         JOIN States as PostalStatesAlias
            ON M.PostalState = PostalStatesAlias.ID
         JOIN Cities as PostalCitiesAlias
            ON M.PostalCity = PostalCitiesAlias.ID
   WHERE
      M.ID = @id

正如 Kenneth 指出的那样，如果任何列在相应的连接表中没有专门找到匹配项，则可能会出现 NULL，它不会返回记录。因此，您可能会将 JOIN 更改为 LEFT JOIN。此外，您提到了“Districts”表，但没有提供，但 DID 提供了您的“Cities”表，这是我用作连接的基础。

Answer 3

在 CountryMaster.Id = dbo.JFPMembers.RegisteredCountry 和 CountryMaster.Id = dbo.JFPMembers.postalCountry 上左加入 CountryMaster

您是指and 还是or？