SQL Server循环和游标[关闭]

Question

我为 SQL Server 继承了以下代码：

SET NOCOUNT ON
DECLARE 
@PERSON_ID AS INT, 
@COMMS_DATE AS DATE,
@PERSON_ID_HOLD AS INT, 
@COMMS_DATE_HOLD AS DATE,
@CAMPAIGN_ID AS INT,
@CAMPAIGN_ID_OLD AS INT,
@SQL AS VARCHAR(200)

SELECT @PERSON_ID_HOLD = 0
SELECT @COMMS_DATE_HOLD = null
SELECT @CAMPAIGN_ID = 0
SELECT @CAMPAIGN_ID_OLD = 0

DECLARE COMMS_CURSOR CURSOR FOR
SELECT PERSONID, ReportDate FROM ##Motability_Comms_Combined order by PersonID, ReportDate

OPEN COMMS_CURSOR
FETCH NEXT FROM COMMS_CURSOR
INTO @PERSON_ID, @COMMS_DATE

WHILE @@FETCH_STATUS = 0
BEGIN
IF (@PERSON_ID = @PERSON_ID_HOLD) and (DATEDIFF(day,@COMMS_DATE_HOLD,@COMMS_DATE) > 90)
BEGIN
IF @CAMPAIGN_ID = 0
begin
SET @PERSON_ID_HOLD = @PERSON_ID
SET @COMMS_DATE_HOLD = @COMMS_DATE
end
ELSE
begin 
SET @CAMPAIGN_ID_OLD = @CAMPAIGN_ID
SET @CAMPAIGN_ID = @CAMPAIGN_ID + 1
END
end
ELSE

IF (@PERSON_ID <> @PERSON_ID_HOLD)-- or (@COMMS_DATE <> @COMMS_DATE_HOLD)
BEGIN
SET @CAMPAIGN_ID = 1
SET @CAMPAIGN_ID_OLD = @CAMPAIGN_ID
END

IF (@CAMPAIGN_ID > 1)
BEGIN
UPDATE ##Motability_Comms_Combined SET Derived_Campaign_ID = @CAMPAIGN_ID WHERE personid = @PERSON_ID AND REPORTDATE = @COMMS_DATE  --WHERE CURRENT OF COMMS_CURSOR
END

SET @PERSON_ID_HOLD = @PERSON_ID
SET @COMMS_DATE_HOLD = @COMMS_DATE
FETCH NEXT FROM COMMS_CURSOR INTO @PERSON_ID, @COMMS_DATE
END

CLOSE COMMS_Cursor
DEALLOCATE COMMS_Cursor

UPDATE ##Motability_Comms_Combined SET Derived_Campaign_ID = 1 WHERE Derived_Campaign_ID is null

SET NOCOUNT OFF

请谁能告诉我这种 SQL 的目的是什么？ nocount、declare、游标等？有没有另一种方法来代替选择？

提前感谢您的帮助。

Answer 1

• SET NOCOUNT ON 将防止返回一条消息，说明更新了多少行。在代码中的某些情况下，这是必要的，因为消息被解释为附加的结果集。此消息还有一些额外的开销。

• CURSORS 用于以程序方式执行操作，而不是通常的基于集合的方式（例如，如果您需要遍历一些数据，为每一行执行存储过程）。它们非常耗费资源，通常不受欢迎。看来这可以在没有光标的情况下重写。

• "##Motability_Comms_Combined 是全局临时表，因此也可能被其他代码引用（在不同的 SQL 连接中）