在子查询上加入 Sqlite 表

Question

我正在尝试加入基于分组列“年份”的 sqlite 表。我从一个返回数据库中所有年份的 select 子句开始，现在我想对同一个表进行子查询以获取各种统计信息并根据年份加入它。以下是我所拥有的。

select strftime('%Y', `date`, 'unixepoch') as `year` from transactions as t

left join (
    select sum(amount) as `expenses`, 
    strftime('%Y', `date`, 'unixepoch') as `year` from transactions
    where type = -1 and user_id = 1
    group by strftime('%Y', `date`, 'unixepoch')
) as e on e.year = t.year

left join (
    select sum(amount) as `income`, 
    strftime('%Y', `date`, 'unixepoch') as `year` from transactions
    where type = 1 and user_id = 1
    group by strftime('%Y', `date`, 'unixepoch')
) as i on i.year = t.year

group by strftime('%Y', `date`, 'unixepoch');

当我尝试运行该 sql 语句时，我得到“没有这样的列：t.year”。为什么我不能根据别名列加入？

Answer 1

表 transactions 别名为 t 不包含列 year（这是一个派生列）。
改为：

select strftime('%Y', t.`date`, 'unixepoch') as `year` from transactions as t

left join (
    select sum(amount) as `expenses`, 
    strftime('%Y', `date`, 'unixepoch') as `year` from transactions
    where type = -1 and user_id = 1
    group by strftime('%Y', `date`, 'unixepoch')
) as e on e.year = strftime('%Y', t.`date`, 'unixepoch')

left join (
    select sum(amount) as `income`, 
    strftime('%Y', `date`, 'unixepoch') as `year` from transactions
    where type = 1 and user_id = 1
    group by strftime('%Y', `date`, 'unixepoch')
) as i on i.year = strftime('%Y', t.`date`, 'unixepoch')

group by strftime('%Y', t.`date`, 'unixepoch');

我想您想要返回的连接表中的其他列虽然不在当前代码中。

我认为这是您想要实现的目标：

select 
  strftime('%Y', t.`date`, 'unixepoch') as `year` ,
  sum(case when type = -1 and user_id = 1 then amount end) as `expenses`,
  sum(case when type = 1 and user_id = 1 then amount end) as `income`
from transactions as t
group by strftime('%Y', t.`date`, 'unixepoch');