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我正在尝试优化包含交叉连接的查询。我有大型查询，我继续与派生表交叉连接。

是否会通过将派生表转换为视图来提高查询速度？或者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，所以不需要全部阅读。要点很简单，就是有一个交叉连接。我是 sql 新手，但有人告诉我交叉连接会减慢速度。

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2 回答 2

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因此，您的交叉联接没什么大不了的，因为第二个内联查询只返回一行。

十字加入“减慢速度”的方式与装载汽车减慢速度的方式相同。

当然可以，但是如果您需要移动的东西，您可以将它们装载到汽车中，如果您需要笛卡尔积，则进行交叉连接。

于 2011-01-28T16:55:23.810 回答
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如果您的问题是交叉连接是否慢？（比什么？；）），那么简化的答案是肯定的。当然，这是对一般问题的非常一般的回答。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（我是一个预言家，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那些并再次检查计划。

注意：如果您发现您的查询解释计划足够好，您不必浪费时间进行进一步分析。

于 2011-01-28T17:19:04.000 回答