怎么在 MySQL 中比较两个查询结果是否相等?
本教程将介绍如何在 MySQL 中比较两个查询结果是否相等?的处理方法，这篇教程是从别的地方看到的，然后加了一些国外程序员的疑问与解答，希望能对你有所帮助，好了，下面开始学习吧。
I'm a MySQL user. I have two queries, and I wish to compare their results for equality. I would like to do this with a single query which would return true or false, so each of my two queries would most likely take the form of sub-queries.
I would like to avoid returning the results from both queries and comparing them at the application level, to cut down on communication and to improve performance. I would also like to avoid looping over the results at the database level if possile, but if there's no other way, so be it.
I have searched high and low for an example on how to do this, but have come up empty handed. Some sample code would be most appreciated, because I'm a newbie to SQL programming. Thanks!
Note: I'm looking for a solution which would work with any two arbitrary queries, so I'm going to refrain from posting what my two queries happen to be.
SELECT CASE WHEN count1 = count2 AND count1 = count3 THEN 'identical' ELSE 'mis-matched' END FROM ( SELECT (SELECT COUNT(*) FROM <query1>) AS count1, (SELECT COUNT(*) FROM <query2>) AS count2, (SELECT COUNT(*) FROM (SELECT * FROM query1 UNION SELECT * FROM query2) AS unioned) AS count3 ) AS counts
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