Question

我必须使用SQL命令（文章管理）维护一个应用程序。

一个查询如下所示：

SET @from_timestamp = '2013-07-01 00:00:00';
SET @serialnumber = '%aaaa01%';

SELECT
    test1.article,
    test1.serialnumber,
    test2.`timestamp` as test2_timestamp,
    test2.additionalinfo,
    test1.`timestamp` AS test1_timestamp,
    test1.text0 AS test1_text0,
    test1.text1 AS test1_text1,
    test1.text2 AS test1_text2,
    test1.text3 AS test1_text,
    test3.text1 as test3_text1,
    test3.`timestamp` AS test3_timestamp,
    test3.`status`,
    TIMESTAMPDIFF(MINUTE, test1.`timestamp`, test3.`timestamp`) as DeltaT
FROM (
    SELECT
        max(`timestamp`) AS TIMESTAMP,
        article,
        serialnumber,
        text1,
        text2,
        text3,
        text4
    FROM exampleTable
    WHERE
        test = 'test1' AND
        `timestamp` >= @from_timestamp AND
        os0 LIKE @serialnumber
    GROUP BY serialnumber
) AS test1
LEFT JOIN (
    SELECT
        max(`timestamp`) AS TIMESTAMP,
        serialnumber,
        status,
        text1
    FROM exampleTable
    WHERE
        test = 'test3' AND
        `timestamp` >= @from_timestamp
    GROUP BY serialnumber
) AS test3 
ON test1.serialnumber = test3.serialnumber
LEFT JOIN (
    SELECT
        max(`timestamp`) AS TIMESTAMP,
        serialnumber,
        article,
        text1
    FROM exampleTable
    WHERE
        LENGTH(serialnumber) = 13 AND
        test = 'test2' AND
        `status` = -1 AND
        `timestamp` >= @from_timestamp
    GROUP BY serialnumber
) AS test2 
ON test1.serialnumber = test2.serialnumber
ORDER BY test1.`timestamp`

它只使用一个保存产品数据的表。但正如预期的那样，这个查询真的很慢。有没有可能的优化？

修改：Attached image of the explain sql result

Edit2：该表有很多数据（最后COUNT（*）提供39589279 ;-)）

Edit3：Attached image of the explain table result

Edit4：请不要责怪我的表格定义，它是由其他人开发的很老的，如果不改变它就不可能改变它。

Answer 1

首先，你要在同一张桌子上查询三次，然后再加入。第一个简化是只使用一个选择：

SELECT
    article,
    serialnumber,
    text1,
    text2,
    text3,
    text4,
    max(case when 
        test = 'test1' AND
        os0 LIKE @serialnumber
    then `timestamp` else null end) AS test1_timestamp,
    max(case when 
        LENGTH(serialnumber) = 13 AND
        test = 'test2' AND
        `status` = -1
    then `timestamp` else null end) AS test2_timestamp,
    max(case when 
        test = 'test3'
    then `timestamp` else null end) AS test3_timestamp,
FROM exampleTable
WHERE
    test in ('test1', 'test2', 'test3') AND
    `timestamp` >= @from_timestamp
GROUP BY serialnumber

这已经给你一个很大的改进。

其次，您必须在timestamp列上添加索引以提高速度。

使用许多子选择优化MySQL查询

1 个答案: