SQLServer MERGE 用法

最新推荐文章于 2024-05-29 09:15:37 发布

暮雪寒寒

最新推荐文章于 2024-05-29 09:15:37 发布

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本文深入探讨SQL Merge语句的使用技巧，通过具体案例展示如何高效地从JSON数据中提取信息并应用于数据库的更新与插入操作。文章涵盖Merge语句的基本语法、常见坑点及官方示例，适合数据库开发者及SQL进阶学习者。

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今天写存储过程的时候，遇到了从一个大json串中取一个id号比对，如果是存在的就更新，不存在就新增。查了资料，觉得还是用merge比较好，这个用法坑也不少，一起来看看代码吧。

MERGE tABatch AS t  -- 需要操作的主体表
USING(
	SELECT batchNo,COUNT(0) AS waitTotal
	FROM (
	SELECT batchNo FROM OPENJSON(@checkJson)
	WITH(batchNo VARCHAR(50) '$.batchNo')
    ) t GROUP BY t.batchNo
	) AS s (batchNo,waitTotal) -- USING里面是数据源，as以后，必须按照顺序指定字段名
    ON t.batchNo = s.batchNo  -- 这里是对比的条件
	WHEN MATCHED THEN 
	-- 如果有匹配就更新,只用写要更新的内容即可
		UPDATE SET t.waitTotal = t.waitTotal+s.waitTotal
	WHEN NOT MATCHED THEN 
	-- 没有匹配就新增,注意这里的INSERT不能再跟表名了
	INSERT  
	(
		batchNo,
		waitTotal,
		createTime
	)VALUES(
		s.batchNo,
		s.waitTotal,
		getdate()
	);
-- merge必须分号结尾,不然报错

上面是我的示例，如果不放心可以来看看官方的：

CREATE PROCEDURE dbo.InsertUnitMeasure  
    @UnitMeasureCode nchar(3),  
    @Name nvarchar(25)  
AS   
BEGIN  
    SET NOCOUNT ON;  
-- Update the row if it exists.      
    UPDATE Production.UnitMeasure  
SET Name = @Name  
WHERE UnitMeasureCode = @UnitMeasureCode  
-- Insert the row if the UPDATE statement failed.  
IF (@@ROWCOUNT = 0 )  
BEGIN  
    INSERT INTO Production.UnitMeasure (UnitMeasureCode, Name)  
    VALUES (@UnitMeasureCode, @Name)  
END  
END;  
GO  
-- Test the procedure and return the results.  
EXEC InsertUnitMeasure @UnitMeasureCode = 'ABC', @Name = 'Test Value';  
SELECT UnitMeasureCode, Name FROM Production.UnitMeasure  
WHERE UnitMeasureCode = 'ABC';  
GO  
  
-- Rewrite the procedure to perform the same operations using the 
-- MERGE statement.  
-- Create a temporary table to hold the updated or inserted values 
-- from the OUTPUT clause.  
CREATE TABLE #MyTempTable  
    (ExistingCode nchar(3),  
     ExistingName nvarchar(50),  
     ExistingDate datetime,  
     ActionTaken nvarchar(10),  
     NewCode nchar(3),  
     NewName nvarchar(50),  
     NewDate datetime  
    );  
GO  
ALTER PROCEDURE dbo.InsertUnitMeasure  
    @UnitMeasureCode nchar(3),  
    @Name nvarchar(25)  
AS   
BEGIN  
    SET NOCOUNT ON;  
   -- 重点看这一段
    MERGE Production.UnitMeasure AS target  
    USING (SELECT @UnitMeasureCode, @Name) AS source (UnitMeasureCode, Name)  
    ON (target.UnitMeasureCode = source.UnitMeasureCode)  
    WHEN MATCHED THEN   
        UPDATE SET Name = source.Name  
WHEN NOT MATCHED THEN  
    INSERT (UnitMeasureCode, Name)  
    VALUES (source.UnitMeasureCode, source.Name)  
    OUTPUT deleted.*, $action, inserted.* INTO #MyTempTable;  
END;  
GO  
-- Test the procedure and return the results.  
EXEC InsertUnitMeasure @UnitMeasureCode = 'ABC', @Name = 'New Test Value';  
EXEC InsertUnitMeasure @UnitMeasureCode = 'XYZ', @Name = 'Test Value';  
EXEC InsertUnitMeasure @UnitMeasureCode = 'ABC', @Name = 'Another Test Value';  
  
SELECT * FROM #MyTempTable;  
-- Cleanup   
DELETE FROM Production.UnitMeasure WHERE UnitMeasureCode IN ('ABC','XYZ');  
DROP TABLE #MyTempTable;  
GO