使用内部联接优化兰特性能

Question

我有一个像这样的SQL查询：

SELECT `users`.`name`, `users`.`username`, `users`.`bio`, `users`.`city`, `users`.`photo` 
FROM (`onlines`) JOIN `users` 
ON `onlines`.`username`=`users`.`username` 
WHERE `users`.`offline_status` = 0 
AND `users`.`perma_ban` = 0 
AND `users`.`is_premium` = 1 
GROUP BY `onlines`.`username` 
ORDER BY RAND() LIMIT 27

我正在使用兰德，但我对表现不满意。如何优化此查询？

我读到了这个：

How can i optimize MySQL's ORDER BY RAND() function?

但我正在使用内部联接，所以这个问题对我没有帮助。

Answer 1

一种方法是添加where子句。因此，如果您知道大约有多少行符合条件，那么您可以减少数据。所以，如果您知道大约1000个，那么在最终order by之前随机抽取大约50个：

and rand()*1000 < 50

当然，您需要估算总数。

Answer 2

首先从If TeamHome_PlayerNumber1.Value = TeamHome_PlayerNumber2.Value Or TeamHome_PlayerNumber1.Value = TeamHome_PlayerNumber3.Value Or TeamHome_PlayerNumber1.Value = TeamHome_PlayerNumber3.Value Or TeamHome_PlayerNumber1.Value = TeamHome_PlayerNumber4.Value Or TeamHome_PlayerNumber1.Value = TeamHome_PlayerNumber5.Value Or TeamHome_PlayerNumber1.Value = TeamHome_PlayerNumber6.Value Or TeamHome_PlayerNumber1.Value = TeamHome_PlayerNumber7.Value Or TeamHome_PlayerNumber1.Value = TeamHome_PlayerNumber8.Value Or TeamHome_PlayerNumber1.Value = TeamHome_PlayerNumber9.Value Or TeamHome_PlayerNumber1.Value = TeamHome_PlayerNumber10.Value Or TeamHome_PlayerNumber1.Value = TeamHome_PlayerNumber11.Value Or TeamHome_PlayerNumber1.Value = TeamHome_PlayerNumber12.Value Or TeamHome_PlayerNumber1.Value = TeamHome_PlayerNumber13.Value Or TeamHome_PlayerNumber1.Value = TeamHome_PlayerNumber14.Value Then MessageBox.Show("Numer zawodnika 1 się powtarza!", "Powtórzenie!", MessageBoxButtons.OK, MessageBoxIcon.Error) ElseIf TeamHome_PlayerNumber2.Value = TeamHome_PlayerNumber3.Value Or TeamHome_PlayerNumber2.Value = TeamHome_PlayerNumber3.Value Or TeamHome_PlayerNumber2.Value = TeamHome_PlayerNumber4.Value Or TeamHome_PlayerNumber2.Value = TeamHome_PlayerNumber5.Value Or TeamHome_PlayerNumber2.Value = TeamHome_PlayerNumber6.Value Or TeamHome_PlayerNumber2.Value = TeamHome_PlayerNumber7.Value Or TeamHome_PlayerNumber2.Value = TeamHome_PlayerNumber8.Value Or TeamHome_PlayerNumber2.Value = TeamHome_PlayerNumber9.Value Or TeamHome_PlayerNumber2.Value = TeamHome_PlayerNumber10.Value Or TeamHome_PlayerNumber2.Value = TeamHome_PlayerNumber11.Value Or TeamHome_PlayerNumber2.Value = TeamHome_PlayerNumber12.Value Or TeamHome_PlayerNumber2.Value = TeamHome_PlayerNumber13.Value Or TeamHome_PlayerNumber2.Value = TeamHome_PlayerNumber14.Value Then MessageBox.Show("Numer zawodnika 2 się powtarza!", "Powtórzenie!", MessageBoxButtons.OK, MessageBoxIcon.Error) ElseIf TeamHome_PlayerNumber3.Value = TeamHome_PlayerNumber4.Value Or TeamHome_PlayerNumber3.Value = TeamHome_PlayerNumber5.Value Or TeamHome_PlayerNumber3.Value = TeamHome_PlayerNumber6.Value Or TeamHome_PlayerNumber3.Value = TeamHome_PlayerNumber7.Value Or TeamHome_PlayerNumber3.Value = TeamHome_PlayerNumber8.Value Or TeamHome_PlayerNumber3.Value = TeamHome_PlayerNumber9.Value Or TeamHome_PlayerNumber3.Value = TeamHome_PlayerNumber10.Value Or TeamHome_PlayerNumber3.Value = TeamHome_PlayerNumber11.Value Or TeamHome_PlayerNumber3.Value = TeamHome_PlayerNumber12.Value Or TeamHome_PlayerNumber3.Value = TeamHome_PlayerNumber13.Value Or TeamHome_PlayerNumber3.Value = TeamHome_PlayerNumber14.Value Then MessageBox.Show("Numer zawodnika 3 się powtarza!", "Powtórzenie!", MessageBoxButtons.OK, MessageBoxIcon.Error) 'And like this to TeamHome_PlayerNumber14.Value End If 随机挑选27个随机usernames，并给出此限制：

users

然后你快完成了。 WHERE `users`.`offline_status` = 0 AND `users`.`perma_ban` = 0 AND `users`.`is_premium` = 1 几乎没有为查询提供任何内容;它所做的就是消除onlines中未显示的任何用户名。所以只需添加

onlines

然后转到提到的链接，或转到my blog，它会更好地扩展。它提供了5个有效的答案。但是，如果不回答更多问题，我无法告诉你哪个答案最适合你的情况。