游标是执行此类操作的唯一选择吗

Question

我正在尝试优化一个长事务，并且我已经看到以下操作完成了很多次：

Declare @myCursor CURSOR FAST_FORWARD FOR
SELECT field1, MIN(COALESCE(field2, -2)) FROM MyTable tempfact
LEFT JOIN MyTable sd
ON tempfact.ID = sd.ID AND sd.TransactionId = @transactionId
WHERE tempfact.SomeField IS NULL
AND tempfact.TransactionId = @transactionId
GROUP BY tempfact.field1

OPEN @myCursor

FETCH NEXT FROM @myCursor INTO @field1Variable, @field2Variable

WHILE @@FETCH_STATUS = 0
BEGIN
   EXEC USP_SOME_PROC @field1Variable, @field2Variable
   FETCH NEXT FROM @myCursor INTO @field1Variable, @field2Variable
END

CLOSE @myCursor
DEALLOCATE @myCursor

USP_SOME_PROC 存储过程的代码如下：

IF NOT EXISTS (SELECT * FROM SomeTable WHERE Field1 = @field1)
BEGIN
   INSERT INTO SomeTable (Field1, Field2)
   VALUES (@field1, @field2)
END

就像我提到的，这是在很多地方完成的，涉及表和字段不同，但想法保持不变，并且我确信，如果不使用游标，可能有一种方法可以提高这些存储过程的性能，并且可能通过使此事务更快，这是我们遇到的死锁问题（一个主题另一篇文章）可能会得到解决。

Answer 1

您可以使用MERGE来实现此目的

;WITH Source AS
(
SELECT field1,
       MIN(COALESCE(field2, -2)) as field2
FROM   MyTable tempfact
       LEFT JOIN MyTable sd
         ON tempfact.ID = sd.ID
            AND sd.TransactionId = @transactionId
WHERE  tempfact.SomeField IS NULL
       AND tempfact.TransactionId = @transactionId
GROUP  BY tempfact.field1  
)
MERGE SomeTable AS T
USING Source S
ON (T.Field1 = S.Field1)


WHEN NOT MATCHED BY TARGET THEN
    INSERT (Field1, Field2)
    VALUES (field1, field2)
    ;

Answer 2

我还没有机会测试这一点，但这应该很接近：您需要从 SELECT 语句插入，但还需要确保 SomeTable 中不存在相应的记录

INSERT INTO SomeTable (Field1, Field2)
SELECT field1, MIN(COALESCE(field2, -2)) 
FROM MyTable tempfact 
    LEFT JOIN MyTable sd ON tempfact.ID = sd.ID AND sd.TransactionId = @transactionId 
    LEFT JOIN SomeTable st ON st.Field1 = tempfact.field1
WHERE tempfact.SomeField IS NULL 
    AND tempfact.TransactionId = @transactionId 
    AND st.Field1 IS NULL
GROUP BY tempfact.field1 

Answer 3

您不需要有光标，可以使用批量插入逻辑，如下所示

INSERT INTO SomeTable (Field1, Field2) 
SELECT 
       field1,       
       MIN(COALESCE(field2, -2)) 
FROM
      MyTable tempfact        
LEFT JOIN 
      MyTable sd          
           ON tempfact.ID = sd.ID             
              AND sd.TransactionId = @transactionId 
WHERE  
      tempfact.SomeField IS NULL        
      AND tempfact.TransactionId = @transactionId 
GROUP  BY 
      tempfact.field1

希望这有帮助！