Mysql 如果没有where子句，如何计算两个不同表中两列的总和？

我使用下面的sql语句对两个不同表中两列的值求和。语句可以输出，但不能输出所需的结果

SELECT
SUM(`_income`.rate) AS Income,
SUM(`_expense`.rate) AS Expense,
SUM(_income.rate)-SUM(_expense.rate) AS Balance
FROM `_expense`, `_income`

我的桌子在这里：

CREATE TABLE IF NOT EXISTS `_expense` (
  `id` int(11) NOT NULL AUTO_INCREMENT,
  `item` varchar(100) CHARACTER SET utf8 COLLATE utf8_unicode_ci NOT NULL,
  `qnty` int(11) NOT NULL,
  `rate` int(11) NOT NULL,
  `date` date NOT NULL,
  `CreatedByPHPRunner` int(11) NOT NULL,
  `remarks` text NOT NULL,
  PRIMARY KEY (`id`)
) ENGINE=MyISAM  DEFAULT CHARSET=latin1 AUTO_INCREMENT=4 ;

--

--表的转储数据

\u费用

---

--

--表收入的表结构 --

--表

的倾销数据\u收入

这应该做到：

select income, expense, income-expense balance
from (select sum(rate) income
      from _income) i
JOIN (select sum(rate) expense
      from _expense) e

这应该做到：

select income, expense, income-expense balance
from (select sum(rate) income
      from _income) i
JOIN (select sum(rate) expense
      from _expense) e

---

我认为您应该在表的并集上求和，其中缺少的列的值为0table@Pleun谢谢你的快速回复。我会尝试一下……我认为您应该在表的并集上求和，其中缺少的列的值为0table@Pleun谢谢你的快速回复。我会试试……非常好。这比在应用程序中执行要好得多非常好。这比在应用程序中执行要好

INSERT INTO `_income` (`id`, `items`, `qnty`, `rate`, `date`, `remarks`, `CreatedByPHPRunner`) VALUES
(1, 'TV chhe siam', 1, 1500, '2013-08-15', 'Ka hniam hrep', NULL),
(2, 'First Star', 1, 25, '2013-08-15', 'A loose-in aw', NULL),
(3, 'Mobile Chhe siam', 2, 200, '2013-08-13', 'Nokia chhuak ho a nia', NULL),
(4, 'Internet hman man', 1, 1500, '2013-08-14', 'Ka net min hman sak a', NULL);

select income, expense, income-expense balance
from (select sum(rate) income
      from _income) i
JOIN (select sum(rate) expense
      from _expense) e