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[英]How to self join a table faster without expensive query (Oracle SQL)
[英]Faster sql query then join
我有一個超過10,000行的大表,在不久的將來它將增長到1,000,000,我需要運行一個查詢,為每個用戶的每個關鍵字返回一個Time值。 我現在有一個很慢,因為我使用左連接,它需要一個子查詢/關鍵字:
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
該表如下所示:
WindowTitle | StartTime | EndTime | User
------------|-----------|---------|---------
Form1 | DateTime | DateTime| user1
Form2 | DateTime | DateTime| user2
... | ... | ... | ...
Form_n | DateTime | DateTime| user_n
輸出應如下所示:
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 | ... | ...
問題是,這是MySQL中最快的方法嗎?
我認為你的通配符搜索可能正在減慢它的速度,因為你無法真正利用這些字段上的索引。 此外,如果您可以避免進行子查詢並且只是進行直接連接,則可能有所幫助,但通配符搜索更糟糕。 無論如何,您是否可以將表更改為具有索引且不需要通配符搜索的categoryName或categoryID? 比如“where categoryName ='Outlook'”
要優化表中的數據,請添加一個categoryID(理想情況下,這將引用一個單獨的表,但在本例中我們只使用任意數字):
alter table rawData add column categoryID int not null
alter table rawData add index (categoryID)
然后填充現有數據的categoryID字段:
update rawData set categoryID=1 where name like '%Outlook%'
update rawData set categoryID=2 where name like '%Facebook%'
-- etc...
然后更改您的插入以遵循相同的規則。
然后像這樣進行SELECT查詢(將通配符更改為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
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