需要帮助来优化SQL查询

Question

我有一个SQL主表CHANNEL_PT ，我想根据其他两个主表CHANNEL和PT进行填充。

在CHANNEL_PT三个colums cosist CHANNEL_PT_CD ， CHANNEL_CD和PT_CD 。

将记录插入CHANNEL_PT的方案是，如果我在CHANNEL表中有两个条目，

PT表中的两个条目如下所示，

那么CHANNEL_PT表将如下所示

我知道可以使用CURSOR来完成此操作，但是由于性能问题，我不使用它。

我已经编写了如下查询以获得预期结果，但想知道任何其他更有效的方法或优化的查询。

BEGIN TRANSACTION
DECLARE @CH INT;
DECLARE @CH_CNT INT;
DECLARE @CH_MAX INT; 
SELECT @CH_MAX = MAX(CHANNEL_CD) FROM CHANNEL;
SELECT @CH = ISNULL(MIN(CHANNEL_CD),0),@CH_CNT=COUNT(CHANNEL_CD) FROM CHANNEL WHERE CHANNEL_CD > -1

WHILE @CH <= @CH_MAX

BEGIN
    DECLARE @PT INT;
    DECLARE @PT_CNT INT;
    DECLARE @PT_MAX INT; 
    SELECT @PT_MAX = MAX(PT_CD) FROM PT;
    SELECT @PT = ISNULL(MIN(PT_CD),0),@PT_CNT=COUNT(PT_CD) FROM PT WHERE PT_CD > -1
    WHILE @PT <=@PT_MAX
        BEGIN
            DECLARE @CPT INT;
            SELECT @CPT = ISNULL(MAX(CHANNEL_PT_CD),0) FROM CHANNEL_PT
            IF NOT EXISTS(SELECT CHANNEL_CD,PT_CD FROM CHANNEL_PT WHERE CHANNEL_CD=@CH and PT_CD=@PT)
                BEGIN
                    INSERT INTO CHANNEL_PT VALUES(@CPT+1,@CH,@PT)
                END
            SELECT @PT = MIN(PT_CD) FROM PT WHERE PT_CD > @PT
        END 
    SELECT @CH=MIN(CHANNEL_CD) FROM CHANNEL WHERE CHANNEL_CD > @CH
END
COMMIT;

Answer 1

听起来您正在描述交叉连接。 CHANNEL_PT_CD列是否定义为IDENTITY列？ 这样一来，您便无需分配该值，因为服务器将为您完成该操作。

然后您可以执行简单的INSERT / SELECT

INSERT INTO CHANNEL_PT
SELECT b.CHANNEL_CD, c.PT
  FROM CHANNEL b 
 cross join PT c

Answer 2

请试试：

DECLARE @CPT INT=0;
SELECT @CPT = ISNULL(MAX(CHANNEL_PT_CD),0) FROM CHANNEL_PT

INSERT INTO CHANNEL_PT
SELECT DISTINCT @CPT+ROW_NUMBER() OVER(ORDER BY b.CHANNEL_CD),
     b.CHANNEL_CD, 
     c.PT
FROM CHANNEL b, PT c
WHERE (SELECT COUNT(*) FROM CHANNEL_PT a 
       WHERE a.CHANNEL_CD=b.CHANNEL_CD AND a.PT_CD=c.PT)=0