MySQL从两个表中用JOIN选择随机行 [英] MySQL select random row with JOIN from two tables

问题描述

几天来我一直在寻找解决这个问题的方法，但找不到任何可以减少运行查询时间的东西.

I've been searching for a solution to this problem for a few days now and could not find anything that would reduce the time it takes to run the query.

我有2张桌子:

"product_db":  
unique_id - [index] 
image 
url_title 
status - [index]

"product_page"
id
product_unique_id - [index]
page_id - [index]

我要选择的是product_db中的随机图像，其中status ='Online'并且产品必须位于页面id = 3

What I want to select is a random image from product_db where status = 'Online' and the product must be in page id = 3

product_db有超过90,000个产品，product_page有超过150000行.

product_db has over 90,000 products and product_page has over 150000 rows.

我现在使用的查询是:

从product_db a选择图像， product_page b WHERE b.page_id = 3 AND a.status ='在线'和a.unique_id = b.product_unique_id ORDER BY RAND() LIMIT 1

SELECT image FROM product_db a, product_page b WHERE b.page_id = 3 AND a.status = 'Online' AND a.unique_id = b.product_unique_id ORDER BY RAND() LIMIT 1

此查询大约需要2.3秒才能运行.网页加载时间很长. 我尝试了其他一些查询，这些查询首先从product_page返回一个具有page_id = 3的随机行，然后查询product_db(它确实减少了所需的时间)，但是问题是我无法比较产品是否为在线"

This query takes around 2.3secs to run. This is quite a long time for a web page to load. I have tried a few other queries that first returns a random row from product_page with page_id = 3 and then querying product_db (it did reduce the time it takes) but the problem with that is I cannot compare if the product is 'Online' or not.

推荐答案

正是这种排序使您放慢了脚步.而不是随机排序，只需选择一个随机product_db.unique_id

It's the sorting that's slowing you down. Rather than sorting by random, just select a random product_db.unique_id

在查询中，将ORDER BY RAND()替换为:

AND product_db.unique_id >= ROUND(RAND()*(SELECT MAX(unique_id) FROM product_db))

如果从数据库中删除了unique_id，请使用而不是>=来使用

.结果的随机性不如按rand排序，但是查询将执行得更快.如果愿意，可以使用=运行多个查询，直到找到一个结果为止，它可能仍然比对所有这些结果进行排序要快得多.

using >= instead of = in case that unique_id has been deleted from the database. Not as random a result as ordering by rand but the query will execute much faster. If you wish, you can run multiple queries with = until a result is found and it still may be quite faster than sorting all those results.

使用显式JOIN将会是:

With an explicit JOIN it would be:

SELECT product_db.image
FROM product_db
JOIN product_page ON product_db.unique_id = product_page.product_unique_id
WHERE product_page.page_id = 3 
AND product_db.status = 'Online' 
AND product_db.unique_id >= ROUND(RAND()*(SELECT MAX(unique_id) FROM product_db))
LIMIT 1

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