如何在 SQL Server 2008 中使用 MERGE 命令从源中删除？

Question

我目前正在使用以下合并代码将日期从源迁移到目标。一旦在目标上执行更新/插入，我有一个新要求来扩展以下代码以从源中删除记录。这是否可能使用合并（我在网上看到的所有示例都在目标而不是源中执行了 del/insert/update）

    MERGE Target1 AS T
USING Source1 AS S
ON (T.EmployeeID = S.EmployeeID) 
WHEN NOT MATCHED BY TARGET AND S.EmployeeName LIKE 'S%' 
    THEN INSERT(EmployeeID, EmployeeName) VALUES(S.EmployeeID, S.EmployeeName)
WHEN MATCHED 
    THEN UPDATE SET T.EmployeeName = S.EmployeeName
WHEN NOT MATCHED BY SOURCE AND T.EmployeeName LIKE 'S%'
    THEN DELETE  ;

Answer 1

在我们的例子中，我们想使用 MERGE 将我们的内部数据库与不同结构的外部源同步。自动 CASCADE 设置不是一种选择，因为我们喜欢许多周期性的关系，而且，实际上，我们不喜欢心怀不满的员工手中的那种廉价权力。在子行消失之前，我们无法删除父行。

所有这些都是通过使用表值参数的闪电般快速的 MERGE 完成的。到目前为止，它们以极低的应用内存开销提供了最佳性能。

为 MERGE of Orders 数据结合分散的建议...

CREATE PROCEDURE MyOrderMerge @SourceValues [MyOrderSqlUserType] READONLY
AS
BEGIN
    DECLARE @LiveRows TABLE (MergeAction VARCHAR(20), OrderId INT);
    DECLARE @DeleteCount INT;

    SET @DeleteCount = 0;

    MERGE INTO [Order] AS [target]

        USING   (   SELECT  sv.OrderNumber,
                    c.CustomerId,
                    st.ShipTypeId
                    sv.OrderDate,
                    sv.IsPriority

                    FROM @SourceValues sv
                        JOIN [Customer] c ON sv.[CustomerName] = c.[CustomerName]
                        JOIN [ShipType] st ON ...
            ) AS [stream]
            ON [stream].[OrderNumber] = [target].[SourceOrderNumber]

        WHEN MATCHED THEN
            UPDATE
                ...

        WHEN NOT MATCHED BY TARGET THEN
            INSERT
                ---

        -- Keep a tally of all active source records
        -- SQL Server's "INSERTED." prefix encompases both INSERTed and UPDATEd rows <insert very bad words here>
        OUTPUT $action, INSERTED.[OrderId] INTO @LiveRows

    ;   -- MERGE has ended

    -- Delete child OrderItem rows before parent Order rows

    DELETE FROM [OrderItem]
        FROM [OrderItem] oi
            -- Delete the Order Items that no longer exist at the source
            LEFT JOIN @LiveRows lr ON oi.[OrderId] = lr.[OrderId]
        WHERE lr.OrderId IS NULL
    ;

    SET @DeleteCount = @DeleteCount + @@ROWCOUNT;

    -- Delete parent Order rows that no longer have child Order Item rows

    DELETE FROM [Order]
        FROM [Order] o
            -- Delete the Orders that no longer exist at the source
            LEFT JOIN @LiveRows lr ON o.[OrderId] = lr.[OrderId]
        WHERE lr.OrderId IS NULL
    ;

    SET @DeleteCount = @DeleteCount + @@ROWCOUNT;

    SELECT MergeAction, COUNT(*) AS ActionCount FROM @LiveRows GROUP BY MergeAction
    UNION
    SELECT 'DELETE' AS MergeAction, @DeleteCount AS ActionCount
    ;
END

一切都在一个甜蜜的循环-dee-loop 流式往返行程中完成，并对关键索引进行了高度优化。即使内部主键值从源中未知，MERGE 操作也使它们可用于 DELETE 操作。

Customer MERGE 使用不同的@LiveRows TABLE 结构，因此使用不同的 OUTPUT 语句和不同的 DELETE 语句...

CREATE PROCEDURE MyCustomerMerge @SourceValues [MyCustomerSqlUserType] READONLY
AS
BEGIN
    DECLARE @LiveRows TABLE (MergeAction VARCHAR(20), CustomerId INT);
    DECLARE @DeleteCount INT;

    SET @DeleteCount = 0;

    MERGE INTO [Customer] AS [target]

        ...

        OUTPUT $action, INSERTED.[CustomerId] INTO @LiveRows

    ;   -- MERGE has ended

    -- Delete child OrderItem rows before parent Order rows

    DELETE FROM [OrderItem]
        FROM [OrderItem] oi
            JOIN [Order] o ON oi.[OrderId] = o.[OrderId]
                -- Delete the Order Items that no longer exist at the source
                LEFT JOIN @LiveRows lr ON o.[CustomerId] = lr.[CustomerId]
        WHERE lr.CustomerId IS NULL
    ;

    SET @DeleteCount = @DeleteCount + @@ROWCOUNT;

    -- Delete child Order rows before parent Customer rows

    DELETE FROM [Order]
        FROM [Order] o
            -- Delete the Orders that no longer exist at the source
            LEFT JOIN @LiveRows lr ON o.[CustomerId] = lr.[CustomerId]
        WHERE lr.CustomerId IS NULL
    ;

    SET @DeleteCount = @DeleteCount + @@ROWCOUNT;

    -- Delete parent Customer rows that no longer have child Order or grandchild Order Item rows

    DELETE FROM [Customer]
        FROM [Customer] c
            -- Delete the Customers that no longer exist at the source
            LEFT JOIN @LiveRows lr ON c.[CustomerId] = lr.[CustomerId]
        WHERE lr.CustomerId IS NULL
    ;

    SET @DeleteCount = @DeleteCount + @@ROWCOUNT;

    SELECT MergeAction, COUNT(*) AS ActionCount FROM @LiveRows GROUP BY MergeAction
    UNION
    SELECT 'DELETE' AS MergeAction, @DeleteCount AS ActionCount
    ;
END

设置和维护有点麻烦 - 但值得收获的效率。

Answer 2

您可以使用输出子句将修改/插入的行捕获到表变量中，并在合并后将其与删除语句一起使用。

DECLARE @T TABLE(EmployeeID INT);

MERGE Target1 AS T
USING Source1 AS S
ON (T.EmployeeID = S.EmployeeID) 
WHEN NOT MATCHED BY TARGET AND S.EmployeeName LIKE 'S%' 
    THEN INSERT(EmployeeID, EmployeeName) VALUES(S.EmployeeID, S.EmployeeName)
WHEN MATCHED 
    THEN UPDATE SET T.EmployeeName = S.EmployeeName
WHEN NOT MATCHED BY SOURCE AND T.EmployeeName LIKE 'S%'
    THEN DELETE  
OUTPUT S.EmployeeID INTO @T;

DELETE Source1
WHERE EmployeeID in (SELECT EmployeeID
                     FROM @T);

Answer 3

你也可以使用下面的代码

drop table energydata

create table temp_energydata  
(
webmeterID int,
DT DateTime ,
kWh varchar(10)
)

Insert into temp_energydata
select 1,getdate()-10, 120
union
select 2,getdate()-9, 140
union
select 3,getdate()-6, 37
union
select 4,getdate()-3, 40
union
select 5,getdate()-1, 240

create table  energydata
(
webmeterID int,
DT DateTime ,
kWh varchar(10)
) 

Insert into energydata (webmeterID,kWh)
select 1, 120
union
select 2, 140
union
select 3, 37
union
select 4, 40

select * from energydata 
select * from temp_energydata

begin tran ABC

DECLARE @T TABLE(ID INT);

MERGE INTO dbo.energydata WITH (HOLDLOCK) AS target
USING dbo.temp_energydata AS source
    ON target.webmeterID = source.webmeterID
    AND target.kWh  = source.kWh 

WHEN MATCHED THEN 
    UPDATE SET target.DT = source.DT

WHEN NOT MATCHED BY source THEN  delete   
 OUTPUT source.webmeterID INTO @T;


DELETE temp_energydata
WHERE webmeterID in (SELECT webmeterID
                     FROM @T);
    --INSERT (webmeterID, DT, kWh)
    --VALUES (source.webmeterID, source.DT, source.kWh)


rollback  tran ABC
commit  tran ABC

Answer 4

很好的响应，但是您的代码将从目标表中删除该行，这是一个示例，您可以在不影响目标表的情况下从源目标中删除行：

if OBJECT_ID('audit.tmp1') IS NOT NULL
    DROP TABLE audit.tmp1   

select *
into audit.tmp1
from 
(
select 1 id, 'aa' nom, convert(date,'2014-01-01') as dd UNION ALL 
select 2 id, 'bb' nom, convert(date,'2013-07-12') as dd UNION ALL 
select 3 id, 'cc' nom, convert(date,'2012-08-21') as dd UNION ALL 
select 4 id, 'dd' nom, convert(date,'2011-11-15') as dd UNION ALL 
select 5 id, 'ee' nom, convert(date,'2010-05-16') as dd ) T


if OBJECT_ID('audit.tmp2') IS NOT NULL
DROP TABLE audit.tmp2   

select *
into audit.tmp2
from 
(
select 1 id, 'aAa' nom, convert(date,'2014-01-14') as dd UNION ALL 
select 2 id, 'bbB' nom, convert(date,'2013-06-13') as dd UNION ALL 
select 4 id, 'dDD' nom, convert(date,'2012-11-05') as dd UNION ALL 
select 6 id, 'FFf' nom, convert(date,'2014-01-12') as dd) T


SELECT * FROM audit.tmp1 order by 1
SELECT * FROM audit.tmp2 order by 1


DECLARE @T TABLE(ID INT);

MERGE audit.tmp2 WITH (HOLDLOCK) AS T
USING (SELECT * FROM audit.tmp1 WHERE nom <> 'dd') AS S
ON (T.id = S.id)
WHEN NOT MATCHED BY TARGET
THEN INSERT(id, nom, dd) VALUES(S.id, S.nom, S.dd)
WHEN MATCHED 
THEN UPDATE SET T.nom = S.nom, T.dd = S.dd
WHEN NOT MATCHED BY SOURCE
THEN UPDATE SET T.id = T.id OUTPUT S.id INTO @T;

DELETE tmp1
FROM audit.tmp1
INNER JOIN
@T AS DEL
    ON DEL.id = tmp1 .id


SELECT * FROM audit.tmp1 ORDER BY 1
SELECT * FROM audit.tmp2 ORDER BY 1

希望对你有帮助。