SQL服務器循環和遊標

Question

我繼承了SQL Server的下面的代碼：

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 

請有誰能夠告訴我這種SQL的目的是如nocount，聲明，遊標，等等？有沒有另一種方式來做選擇呢？

感謝您提前提供任何幫助。

Answer 1

• SET NOCOUNT ON將阻止返回消息說明有多少行被更新。在代碼中的某些情況下，這是必要的，因爲該消息被解釋爲附加的結果集。此消息還有一些額外開銷。

• CURSORS用於以過程方式執行操作，而不是通常的基於集合的方式（例如，如果您需要循環執行一些數據，爲每行執行存儲過程）。他們非常耗費資源，而且通常會皺眉。看起來，這可以在沒有遊標的情況下被重寫。

• 「## Motability_Comms_Combined是全局臨時表，所以也可以通過其他的代碼被稱爲（在不同的SQL連接）