Question

我想显示一个计算两个自定义列的列。

它看起来像这样

SELECT to_account as account, 
SUM(amount) total_claimed, 
COUNT(*) as transaction_count, 
((SELECT time FROM transactions WHERE to_account = account ORDER BY time DESC LIMIT 1) 
- (SELECT time FROM transactions WHERE to_account = account LIMIT 1)) / 3600 as interval_hours, 
(transaction_count / interval_hours) as avg_per_hour 
FROM transactions 
WHERE type='CLAIM' group by to_account ORDER BY COUNT(*)

我收到了消息＆＃34;未知列＆＃39;时间＆＃39;在字段列表＆＃34;

如何使用自定义列？

Answer 1

你应该使用列本身而不是别名，因为它不像

那样可以访问

SELECT COUNT(*) as amount, 
`time` as thetime, 
(`time` / amount) as average 
FROM table WHERE..

（或）在外部查询中完成它，如

SELECT *, (thetime / amount) as average
FROM (
SELECT COUNT(*) as amount, 
(SELECT time FROM table ...) as thetime
 FROM table WHERE...)XXX;

根据您编辑的帖子，您再次使用相同的表达式（OR）获取外部查询中的自定义列，如

SELECT *, (transaction_count / interval_hours) as avg_per_hour
FROM (
SELECT to_account as account, 
SUM(amount) total_claimed, 
COUNT(*) as transaction_count, 
((SELECT time FROM transactions WHERE to_account = account ORDER BY `time` DESC LIMIT 1) 
- (SELECT `time` FROM transactions WHERE to_account = account LIMIT 1)) / 3600 as interval_hours
FROM transactions 
WHERE type='CLAIM' 
group by to_account 
ORDER BY COUNT(*)
) tbl

在MySQL中选择一个自定义列

1 个答案: