MySQL嵌套，嵌套子查询未获取外部变量
MySQL nested, nested subquery not getting outter variable

尝试加入而不是使用嵌套的相关子查询：

SELECT spendings.id, spendings.price, spendings.title, 
      dates.date, users.username, currencies.value,
      y.sum_price
FROM spendings, dates, users, currencies
JOIN (
    SELECT day, SUM(sum_table.price) As sum_price
    FROM (
        SELECT day(d.date) As day,
               s.price
        FROM spendings s, dates d
        WHERE s.date_id = d.id 
          AND day(d.date) = 25
        LIMIT 2 OFFSET 0
    ) sum_table
    GROUP BY day
) y
ON y.day = day(dates.date)
WHERE spendings.date_id = dates.id 
  -- AND day(dates.date) = 25 <== commented since it's redundant now
  AND spendings.user_id = users.id 
  AND spendings.curr_id = currencies.id

一些说明：

不建议对逗号使用旧的FROM table1,table2,table2 WHERE语法： FROM table1,table2,table2 WHERE
表示连接的推荐方式是“新的” ANSI SQL连接语法：

FROM table1
[left|right|cross|[full] outer|natural] JOIN table2 {ON|USING} join_condition1
[left|right|cross|[full] outer|natural] JOIN table3 {ON|USING} join_condition2
....

实际上，这种“新语法”现在已经很老了，因为据我所记得，它是在1992年-22年前发布的。 在IT行业中，22年就像22岁。