在SQL中具有一对多关系的两个表之间建立一对一关系

Question

我有这些疑问：

SELECT        
    dbo.Lines.Unit, dbo.Lines.LineNumber, dbo.Lines.DocumentNumber, 
    dbo.BaseMaterials.Name AS MaterialName, 
    dbo.MaterialDescriptions.Name AS MaterialDescription, 
    dbo.MaterialDescriptions.Description, 
    dbo.MaterialScopes.ScopeName, dbo.MaterialScopeObjectNames.ObjectName, 
    dbo.MaterialDescriptions.Size1, dbo.MaterialDescriptions.Size2, 
    dbo.MaterialDescriptions.ItemCode, dbo.Materials.Quantity, 
    dbo.Materials.Discipline, dbo.Materials.Id, dbo.Lines.Id AS LineId
FROM
    dbo.Materials 
INNER JOIN
    dbo.Lines ON dbo.Materials.LineId = dbo.Lines.Id 
INNER JOIN
    dbo.BaseMaterials ON dbo.Lines.BaseMaterialId = dbo.BaseMaterials.Id 
INNER JOIN
    dbo.MaterialDescriptions ON dbo.Materials.MaterialDescriptionId = dbo.MaterialDescriptions.Id 
INNER JOIN
    dbo.MaterialScopes ON dbo.MaterialDescriptions.MaterialScopeId = dbo.MaterialScopes.Id 
INNER JOIN
    dbo.MaterialScopeObjectNames ON dbo.MaterialDescriptions.MaterialScopeObjectId = dbo.MaterialScopeObjectNames.Id

它返回 16000 条记录。我有另一个名称为joints 的表与lineId 上的material 表有关系，每个material 可以有multi joints，所以当我添加joints 表时我的查询是这样的：

SELECT        
    dbo.Lines.Unit, dbo.Lines.LineNumber, dbo.Lines.DocumentNumber, 
    dbo.BaseMaterials.Name AS MaterialName, 
    dbo.MaterialDescriptions.Name AS MaterialDescription, 
    dbo.MaterialDescriptions.Description, dbo.MaterialScopes.ScopeName, 
    dbo.MaterialScopeObjectNames.ObjectName, dbo.MaterialDescriptions.Size1, 
    dbo.MaterialDescriptions.Size2, dbo.MaterialDescriptions.ItemCode, 
    dbo.Materials.Quantity, dbo.Materials.Discipline, dbo.Materials.Id, 
    dbo.Lines.Id AS LineId, dbo.Joints.TestPackageId
FROM
    dbo.Materials 
INNER JOIN
    dbo.Lines ON dbo.Materials.LineId = dbo.Lines.Id 
INNER JOIN
    dbo.BaseMaterials ON dbo.Lines.BaseMaterialId = dbo.BaseMaterials.Id 
INNER JOIN
    dbo.MaterialDescriptions ON dbo.Materials.MaterialDescriptionId = dbo.MaterialDescriptions.Id 
INNER JOIN
    dbo.MaterialScopes ON dbo.MaterialDescriptions.MaterialScopeId = dbo.MaterialScopes.Id 
INNER JOIN
    dbo.MaterialScopeObjectNames ON dbo.MaterialDescriptions.MaterialScopeObjectId = dbo.MaterialScopeObjectNames.Id 
INNER JOIN
    dbo.Joints ON dbo.Materials.LineId = dbo.Joints.LineId

正如您在最后一行中看到的，我在joints 和materials 之间进行了连接，以访问joints 表中的testpackageid 列。但我的结果返回 220000 条记录。如何更改连接类型我意思是 left 或 right 只返回带有 testpackageId 的 16000 记录

Answer 1

您不能使用JOIN。但是，您可以使用CROSS APPLY：

FROM . . .
     dbo.MaterialScopeObjectNames
     ON dbo.MaterialDescriptions.MaterialScopeObjectId = dbo.MaterialScopeObjectNames.Id CROSS APPLY
     (SELECT TOP 1 j.*
      FROM dbo.Joints j
      WHERE dbo.Materials.LineId = j.LineId
     ) J

通常，您在使用 TOP 时会包含一个 ORDER BY，因此您可以对返回的行进行一些控制。

还要注意，表别名的使用使查询更易于编写和阅读。

Answer 2

您只需一个子查询就可以很容易地得到它。保持您的查询不变，并添加一个子查询以从 Joints 获取该信息。

SELECT        dbo.Lines.Unit, dbo.Lines.LineNumber, dbo.Lines.DocumentNumber, dbo.BaseMaterials.Name AS MaterialName, dbo.MaterialDescriptions.Name AS MaterialDescription, dbo.MaterialDescriptions.Description, 
                         dbo.MaterialScopes.ScopeName, dbo.MaterialScopeObjectNames.ObjectName, dbo.MaterialDescriptions.Size1, dbo.MaterialDescriptions.Size2, dbo.MaterialDescriptions.ItemCode, dbo.Materials.Quantity, 
                         dbo.Materials.Discipline, dbo.Materials.Id, dbo.Lines.Id AS LineId,
                         (select top 1 dbo.Joints.TestPackageId from dbo.Joints where dbo.Joints.LineId = dbo.Materials.LineId)
FROM            dbo.Materials INNER JOIN
                         dbo.Lines ON dbo.Materials.LineId = dbo.Lines.Id INNER JOIN
                         dbo.BaseMaterials ON dbo.Lines.BaseMaterialId = dbo.BaseMaterials.Id INNER JOIN
                         dbo.MaterialDescriptions ON dbo.Materials.MaterialDescriptionId = dbo.MaterialDescriptions.Id INNER JOIN
                         dbo.MaterialScopes ON dbo.MaterialDescriptions.MaterialScopeId = dbo.MaterialScopes.Id INNER JOIN
                         dbo.MaterialScopeObjectNames ON dbo.MaterialDescriptions.MaterialScopeObjectId = dbo.MaterialScopeObjectNames.Id