用平均列更新记录

本文介绍了用平均列更新记录的处理方法，对大家解决问题具有一定的参考价值，需要的朋友们下面随着小编来一起学习吧！ 问题描述

我正在寻找status = 0的一列平均值，并将其更新到该表的另一条记录中. 这是我正在尝试使用的查询.

I'm looking to find the average of a column where status=0 and update it onto another record into that table. This is the query i'm attempting to use.

UPDATE mc25778 set balance=(AVG(balance WHERE status=0)) WHERE username="Average"

尝试执行此任务时出现此错误:

I get this error when trying to perform this task:

Err] 1064 - 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 'WHERE status=0)) WHERE username="Average"' at line 1

有什么办法可以解决这个问题吗?

Any ideas how I can sort this out?

谢谢！

推荐答案

您可以将表与子查询连接，该子查询分别计算每个用户名的平均值，

you can join the table with a subquery which separately calculate the average for every username,

UPDATE mc25778 a INNER JOIN ( SELECT username, AVG(balance) avg_bal FROM mc25778 WHERE status = 0 GROUP BY username ) b ON a.username = b.username SET a.balance = b.avg_bal WHERE a.username = 'Average'

更新1

您似乎想计算所有具有status = 0的记录的总平均值，其结果将在Average的记录上更新

It looks like you want to calculate the total average for all records having status = 0 and the result of it will be updated on the record of Average

UPDATE mc25778 a CROSS JOIN ( SELECT AVG(balance) avg_bal FROM mc25778 WHERE status = 0 ) b SET a.balance = b.avg_bal WHERE a.username = 'Average'

• SQLFiddle演示
• SQLFiddle Demo