Question

我正在尝试优化包含交叉连接的查询。我有一个大的查询，我继续与派生表交叉连接。

是否可以通过将派生表转换为视图来提高查询速度？甚至在永久表中捕获这些信息？

这是我的查询

SELECT  VIEWER_ID, 
        QUESTION_ID, 
        ANSWER_ID, 
        sum(ANSWER_SCORE) AS ANSWER_SCORE_SUMMED
FROM(SELECT  cr.COMMUNICATIONS_ID AS ANSWER_ID, 
        cr.CONSUMER_ID as VIEWER_ID,
        nc.PARENT_COMMUNICATIONS_ID AS QUESTION_ID,
        case when  cr.CONSUMER_ID= nc.SENDER_CONSUMER_ID then 3*((24/(((UNIX_TIMESTAMP(NOW())-UNIX_TIMESTAMP(cal.LAST_MOD_TIME)+3600)/3600))*(ces.EXPERT_SCORE * cirm.CONSUMER_RATING) + (12.5 * scs.SIMILARITY)* (1 - EXP(-0.5 * (cal.TIPS_AMOUNT / ATV.AVG_TIPS)) + .15)))
            else ((24/(((UNIX_TIMESTAMP(NOW())-UNIX_TIMESTAMP(cal.LAST_MOD_TIME)+3600)/3600))*(ces.EXPERT_SCORE * cirm.CONSUMER_RATING) + (12.5 * scs.SIMILARITY)* (1 - EXP(-0.5 * (cal.TIPS_AMOUNT / ATV.AVG_TIPS)) + .15)))
        end as ANSWER_SCORE
FROM (SELECT 234 AS CONSUMER_ID, 
             ACTION_LOG_ID, 
            COMMUNICATIONS_ID 
     FROM consumer_action_log 
     WHERE COMM_TYPE_ID=4) AS cr
JOIN network_communications AS nc 
    ON cr.COMMUNICATIONS_ID=nc.COMMUNICATIONS_ID
JOIN consumer_action_log AS cal 
    ON cr.ACTION_LOG_ID=cal.ACTION_LOG_ID
JOIN communication_interest_mapping AS cim 
    ON nc.PARENT_COMMUNICATIONS_ID=cim.COMMUNICATION_ID
JOIN consumer_interest_rating_mapping AS cirm 
    ON cr.CONSUMER_ID=cirm.CONSUMER_ID
    AND cim.CONSUMER_INTEREST_EXPERT_ID=cirm.CONSUMER_INTEREST_ID
JOIN consumer_expert_score AS ces 
    ON nc.SENDER_CONSUMER_ID=ces.CONSUMER_ID
    AND cim.CONSUMER_INTEREST_EXPERT_ID=ces.CONSUMER_EXPERT_ID
JOIN survey_customer_similarity AS scs 
    ON cr.CONSUMER_ID=scs.CONSUMER_ID_2 
    AND cal.SENDER_CONSUMER_ID=scs.CONSUMER_ID_1 
    OR cr.CONSUMER_ID=scs.CONSUMER_ID_1 
    AND cal.SENDER_CONSUMER_ID=scs.CONSUMER_ID_2
CROSS JOIN
    (
        SELECT AVG(cal.TIPS_AMOUNT) AS AVG_TIPS
        FROM CONSUMER_ACTION_LOG AS cal
        JOIN (SELECT 234 AS CONSUMER_ID, 
                     ACTION_LOG_ID, 
                     COMMUNICATIONS_ID 
              FROM consumer_action_log 
              WHERE COMM_TYPE_ID=4) AS cr 
        ON cal.SENDER_CONSUMER_ID=cr.consumer_id
    ) ATV) AS ASM
GROUP BY ANSWER_ID
ORDER BY ANSWER_SCORE_SUMMED DESC;

这是一个很长的查询，因此无需全部阅读。要点只是有一个交叉连接。我是sql的新手，但我被告知十字加入会降低速度。

Answer 1

因此，您的交叉连接并不是什么好事，因为第二个内联查询只返回一行。

十字加入“减慢速度”的方式与加载汽车的速度相同。

当然，但如果您需要移动的东西，请将它们装入汽车，如果您需要笛卡尔积，则可以进行交叉连接。

Answer 2

如果你的问题是Cross Cross慢了吗？（比什么？;）），那么简化的答案是肯定的。当然，这是对一般问题的一般回答。但对你来说，你需要量化有多慢。

出于所有实际目的，您的查询可能会尽可能快。所以要验证，在你的查询上运行解释计划（我是一个oracle人，但我认为在mysql中运行解释计划并没有那么不同。链接http://dev.mysql.com/doc/refman/5.0/en/explain.html）。

然后创建一个临时表并替换查询中的表并再次检查计划。

注意：如果您发现查询的解释计划足够好，则不必浪费时间进行进一步分析。

消除SQL中的交叉连接

2 个答案: