mysql - 更快的 sql 查询然后加入

Question

我有一个超过 10,000 行的大表，在不久的将来它将增长到 1,000,000 行，我需要运行一个查询，为每个用户返回每个关键字的时间值。我现在有一个非常慢，因为我使用左连接并且它需要一个子查询/关键字:

SELECT rawdata.user, t1.Facebook_Time, t2.Outlook_Time, t3.Excel_time
FROM
rawdata left join
(SELECT user, sec_to_time(SuM(time_to_sec(EndTime-StartTime))) as 'Facebook_Time'
FROM rawdata 
WHERE MainWindowTitle LIKE '%Facebook%'
GROUP by user)t1 on rawdata.user = t1.user left join
(SELECT user, sec_to_time(SuM(time_to_sec(EndTime-StartTime))) as 'Outlook_Time'
FROM rawdata 
WHERE MainWindowTitle LIKE '%Outlook%'
GROUP by user)t2 on rawdata.user = t2.user left join
(SELECT user, sec_to_time(SuM(time_to_sec(EndTime-StartTime))) as 'Excel_Time'
FROM rawdata 
WHERE MainWindowTitle LIKE '%Excel%'
GROUP by user)t3 on rawdata.user = t3.user

表格如下所示:

WindowTitle | StartTime | EndTime | User
------------|-----------|---------|---------
Form1       | DateTime  | DateTime| user1
Form2       | DateTime  | DateTime| user2
...         | ...       | ...     | ...
Form_n      | DateTime  | DateTime| user_n

输出应该是这样的:

User   | Keyword   | SUM(EndTime-StartTime)
-------|-----------|-----------------------
User1  | 'Facebook'|              00:34:12
User1  | 'Outlook' |              00:12:34
User1  | 'Excel'   |              00:43:13
User2  | 'Facebook'|              00:34:12
User2  | 'Outlook' |              00:12:34
User2  | 'Excel'   |              00:43:13
...    | ...       | ...  
User_n | ...       | ...

问题是，在 MySQL 中哪种方式最快？

Answer 1

我认为您的通配符搜索可能是最慢的原因，因为您无法真正利用这些字段上的索引。此外，如果您可以避免进行子查询而直接进行连接，这可能会有所帮助，但通配符搜索要糟糕得多。无论如何，您是否可以将表更改为具有可以具有索引且不需要通配符搜索的 categoryName 或 categoryID？比如“where categoryName = 'Outlook'”

要优化表中的数据，请添加一个类别 ID(理想情况下这将引用一个单独的表，但我们在此示例中使用任意数字):

alter table rawData add column categoryID int not null

alter table rawData add index (categoryID)

然后为现有数据填充 categoryID 字段:

update rawData set categoryID=1 where name like '%Outlook%'
update rawData set categoryID=2 where name like '%Facebook%'
-- etc...

然后更改您的插入内容以遵循相同的规则。

然后像这样进行 SELECT 查询(将通配符更改为 categoryID):

SELECT rawdata.user, t1.Facebook_Time, t2.Outlook_Time, t3.Excel_time
FROM
rawdata left join
(SELECT user, sec_to_time(SuM(time_to_sec(EndTime-StartTime))) as 'Facebook_Time'
FROM rawdata 
WHERE categoryID = 2
GROUP by user)t1 on rawdata.user = t1.user left join
(SELECT user, sec_to_time(SuM(time_to_sec(EndTime-StartTime))) as 'Outlook_Time'
FROM rawdata 
WHERE categoryID = 1
GROUP by user)t2 on rawdata.user = t2.user left join
(SELECT user, sec_to_time(SuM(time_to_sec(EndTime-StartTime))) as 'Excel_Time'
FROM rawdata 
WHERE categoryID = 3
GROUP by user)t3 on rawdata.user = t3.user