如何使用动态表和字段名称连接数据

Question

所以我有一些表包含一个外键，根据上下文引用不同的表和字段。我有一个关键的源表，其中包含相关的表和字段名称。然后，我需要能够查找这些表/字段中的值。

我把它简化为示范下表/数据我有：

CREATE TABLE [dbo].[WorkOrderStatus](
    [WorkOrderStatusId] [int] IDENTITY(1,1) NOT NULL, 
    [Name] [nvarchar](60) NOT NULL 
) ON [PRIMARY] 

CREATE TABLE [dbo].[Note](
    [NoteId] [int] IDENTITY(1,1) NOT NULL, 
    [NoteKeySourceId] [int] NULL, 
    [KeyValue] [int] NULL, 
    [Note] [nvarchar](max) NOT NULL, 
) ON [PRIMARY] 

CREATE TABLE [dbo].[NoteKeySource](
    [NoteKeySourceId] [int] IDENTITY(1,1) NOT NULL, 
    [SourceTable] [nvarchar](60) NOT NULL, 
    [SourceField] [nvarchar](60) NOT NULL, 
    [SourceTextField] [nvarchar](60) NOT NULL, 
) ON [PRIMARY] 

GO 

INSERT INTO WorkOrderStatus VALUES('Open') 
DECLARE @OpenStatusId int = SCOPE_IDENTITY(); 

INSERT INTO WorkOrderStatus VALUES('Closed') 
DECLARE @ClosedStatusId int = SCOPE_IDENTITY(); 

INSERT INTO NoteKeySource VALUES('WorkOrderStatus', 'WorkOrderStatusId', 'Name') 
DECLARE @WorkOrderSource int = SCOPE_IDENTITY(); 

INSERT INTO Note VALUES(@WorkOrderSource, @OpenStatusId, 'Opened the work order') 
INSERT INTO Note VALUES(@WorkOrderSource, @ClosedStatusId, 'Closed the work order') 

所以我需要能够查询说明的列表，包括SourceTextField在NoteKeySource提到，通过鉴定核心价值。

这里是我现在的SP，其工作原理：

CREATE PROCEDURE [dbo].[spGetNotes] 
AS 
SET TRANSACTION ISOLATION LEVEL READ UNCOMMITTED 

CREATE TABLE #NoteTable (
    NoteId int NOT NULL, 
    SourceTable nvarchar(60), 
    SourceField nvarchar(60), 
    SourceTextField nvarchar(60), 
    KeyValue int, 
    Context nvarchar(MAX), 
    Note nvarchar(MAX), 
) 

INSERT INTO #NoteTable (NoteId, SourceTable, SourceField, SourceTextField, KeyValue, Note) 
    SELECT N.NoteId, NKS.SourceTable, NKS.SourceField, NKS.SourceTextField, N.KeyValue, N.Note 
     FROM Note AS N 
      LEFT OUTER JOIN NoteKeySource AS NKS 
       ON NKS.NoteKeySourceId = N.NoteKeySourceId 

DECLARE @Context nvarchar(max) 

DECLARE @Sql nvarchar(255); 
DECLARE @SqlDecl nvarchar(255) = N'@Key int, @Ctx nvarchar(MAX) OUTPUT'; 


DECLARE @NoteId int, @KeyValue int, @SourceTable nvarchar(60), @SourceField nvarchar(60), @SourceTextField nvarchar(60) 

DECLARE db_cursor CURSOR FOR SELECT SourceTable, SourceField, SourceTextField, KeyValue 
     FROM #NoteTable WHERE SourceTable IS NOT NULL FOR UPDATE OF Context 


OPEN db_cursor 
FETCH NEXT FROM db_cursor INTO @SourceTable, @SourceField, @SourceTextField, @KeyValue 

WHILE @@FETCH_STATUS = 0 
BEGIN 
    SET @Sql = N'SELECT @Ctx = ' + @SourceTextField + ' FROM ' + @SourceTable + ' WHERE ' + @SourceField + '= @Key'; 

    EXECUTE sp_executesql @Sql, @SqlDecl, @Key = @KeyValue, @Ctx = @Context OUTPUT 

    UPDATE #NoteTable SET Context=@Context WHERE CURRENT OF db_cursor 

    FETCH NEXT FROM db_cursor INTO @SourceTable, @SourceField, @SourceTextField, @KeyValue 
END 

CLOSE db_cursor 
DEALLOCATE db_cursor 


SELECT NoteId, Context, Note from #NoteTable 

DROP TABLE #NoteTable 

RETURN 0 

调用spGetNotes回报：

1：打开：打开工作秩序

2：关闭：关闭工作order

它的工作原理，但它非常丑陋，我只想知道是否有一个更好/更清洁/更合适的方式来做到这一点，而不使用游标或while循环。我的理解是，动态SQL不能用于普通SQL的子查询中，所以这是我能想到的最好的。

当谈到SQL时，我相对比较环保，所以如果我错了，请赐教！另外，如果对总体领域问题有更好的整体解决方案，那么也会受到欢迎和赞赏:)

Answer 1

创建一个视图，在源表中提供单个EAV叠加层。然后将NoteKeySource连接到它。

CREATE VIEW AllSources AS (
    SELECT 
    'SourceTable1' AS [SourceTable], [SourceField], [SourceTextField] 
    FROM SourceTable1 
    UNPIVOT([SourceTextField] FOR [SourceField] IN 
     ('Table1Field1','Table1Field2','Table1Field3','Table1Field4') 
) p 
    UNION ALL 
    SELECT 
    'SourceTable2' AS [SourceTable], [SourceField], [SourceTextField] 
    FROM SourceTable2 
    UNPIVOT([SourceTextField] FOR [SourceField] IN 
    ('Table2Field1','Table2Field2') 
) p 
    UNION ALL 
    SELECT 
    'SourceTable3' AS [SourceTable], [SourceField], [SourceTextField] 
    FROM SourceTable3 
    UNPIVOT([SourceTextField] FOR [SourceField] IN 
    ('Table3Field1','Table3Field2','Table3Field3') 
) p 
    --etc 
)