優化sql查詢，即使對小數據也太慢

Question

基本上，我試圖從匹配每個URL的單詞中獲取計數的總和。 我有這個SQL查詢：

select w.url, w.word, w.count, (
select sum(w2.count)
from wordcounts w2 where w2.url = w.url and w2.word in ('search', 'more')
) as totalcount
from wordcounts w
where w.word in ('search', 'more')

我正在使用此查詢來獲得這種結果：

URL                              |  word  | count | Total Count

http://haacked.com/              | more   | 61    | 62
http://haacked.com/              | search | 1     | 62
http://feeds.haacked.com/haacked | more   | 58    | 59
http://feeds.haacked.com/haacked | search | 1     | 59
http://www.asp.net/privacy       | more   | 7     | 13
http://www.asp.net/privacy       | search | 6     | 13

我原來的表結構是

ID | URL  |  word  | count

但是問題是，這個小的查詢要花費太多時間。 7秒鍾以上即可在數千行上運行以上查詢。 如何優化此查詢？

我從另一個站點獲得了此語法，但是它給出了錯誤。

select id, url, word, count, 
sum(count) over(partition by url) as count_sum
from wordcounts where word in ('search', 'more') order by url

Error code 1064, SQL state 42000: You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near '(partition by url) as count_sum
from wordcounts where word in ('search', 'more')' at line 2
Line 1, column 1

Execution finished after 0 s, 1 error(s) occurred.

Answer 1

預匯總：

select w.url, w.word, w.`count`, w3.totalcount
from wordcounts w
join (
     select w2.url, sum(w2.`count`) totalcount
     from wordcounts w2
     where w2.word in ('search', 'more')
     group by w2.url) w3 on w3.url = w.url
where w.word in ('search', 'more')

Answer 2

使用JOIN而不是子查詢：

select w.url, w.word, w.count, sum(w2.count) as totalcount 
from wordcounts w
left join wordcounts w2  
  on w2.url = w.url and w2.word in ('search', 'more')
where w.word in ('search', 'more')
group by w.url, w.word, w.count

Answer 3

您最初的查詢在MySQL中運行緩慢，因為MySQL正在為結果集的每一行執行子查詢。 您可以通過執行一次匯總並將結果加入以下內容來解決此問題：

select w.url, w.word, w.count, wsum.sumcount
from wordcoutns w join
     (select w.url, w.word, SUM(w.count) as sumcount
      from wordcounts w
      where w.word in ('search', 'more')
      group by w.url, w.word
     ) wsum
     on wsum.url = w.url and wsum.word = w.word
where w.word in ('search', 'more') 

其他數據庫支持一類稱為窗口函數的函數，這使此操作變得更加容易。 MySQL不支持這些。