sql - SQL 中派生表的性能问题

Question

我在使用 MySQL 中的派生表时遇到问题。使用派生表本质上会减慢查询的处理速度吗？

这是我尝试运行的查询。它不会执行并且只是超时。

确实成功了。确实，我已将问题隔离到最后一次加入。当我取出最后一个连接时，它工作正常。但是当我将最后一个连接添加回来时，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;

Answer 1

希望这有帮助...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comm_type_id 为4 的所有记录。似乎没有返回到其他表的连接。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;