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我在 MySQL 中使用派生表时遇到问题。使用派生表是否会固有地减慢查询的处理速度？

这是我要运行的查询。它不会执行，只是超时。

它确实成功了。真的，我已将问题隔离到最后一次加入。当我取出最后一个加入时，它工作正常。但是当我添加最后一个连接时，它拒绝执行。

SELECT cr.COMMUNICATIONS_ID AS ANSWER_ID, 
       cr.CONSUMER_ID as VIEWER_ID, 
       cr.ACTION_LOG_ID, 
       nc.PARENT_COMMUNICATIONS_ID AS QUESTION_ID, 
       nc.SENDER_CONSUMER_ID AS REPLIER_ID, 
       ces.EXPERT_SCORE AS REPLIER_EXPERTISE, 
       cim.CONSUMER_INTEREST_EXPERT_ID AS DOMAIN
    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 communication_interest_mapping AS cim ON 
nc.PARENT_COMMUNICATIONS_ID=cim.COMMUNICATION_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;
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2 回答 2

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希望这会有所帮助......这是一些 mysql CREATE INDEX 语句。基本上，如果您可以添加索引，请确保有一个索引覆盖连接 2 个或更多表的每个列。

CREATE INDEX idx_nc
ON network_communications(COMMUNICATIONS_ID);

CREATE INDEX idx_cim
ON communication_interest_mapping(COMMUNICATION_ID);

CREATE INDEX idx_ces
ON consumer_expert_score(CONSUMER_ID, CONSUMER_EXPERT_ID);

派生表本身并不坏，但在这种情况下（见下文），您将从 consumer_action_log 中提取所有 comm_type_id 为 4 的记录。似乎没有与其他表的连接。这可能是 sql 永远不会返回的原因。

SELECT cr.COMMUNICATIONS_ID, 
           cr.CONSUMER_ID, 
           cr.ACTION_LOG_ID, 
           nc.PARENT_COMMUNICATIONS_ID, 
           nc.SENDER_CONSUMER_ID, 
           ces.EXPERT_SCORE, 
           cim.CONSUMER_INTEREST_EXPERT_ID

    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 communication_interest_mapping AS cim ON 
         nc.PARENT_COMMUNICATIONS_ID=cim.COMMUNICATION_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;
于 2011-01-27T14:30:32.277 回答
1

除了 John 在 anser 中指出的查找表中应该存在的索引之外，我会确保您的 consumer_action_log 表中的 COMM_TYPE_ID 也有索引。

然后，在您的子句中添加一个关键字...当查询组织良好而不是依靠查询引擎进行优化时，我总是看到很好的结果...在这里查看另一个示例

SELECT STRAIGHT_JOIN
         cr.COMMUNICATIONS_ID AS ANSWER_ID,
         cr.CONSUMER_ID as VIEWER_ID,  
         etc... rest of your query...

可能是优化器正在尝试查看其他表以找出要获取的内容。请参阅我提供的其他 StackOverflow 答案中的评论链接。

于 2011-01-27T14:52:56.407 回答