mySQL將相同列中的兩個值分開

Question

我希望使用mySQL從同一列中划分值。

這有更好的方法嗎？ 我真的需要3個選擇語句嗎？

SELECT (SELECT FixAM From Fixes WHERE Id = 1) / (SELECT FixAM From Fixes WHERE Id = 2)

我的表結構如下：

CREATE TABLE IF NOT EXISTS `Fixes` (
  `Id` int(11) NOT NULL AUTO_INCREMENT COMMENT 'PK',
  `CurrencyId` int(11) NOT NULL COMMENT 'FK',
  `MetalId` int(11) NOT NULL COMMENT 'FK',
  `FixAM` decimal(10,5) NOT NULL,
  `FixPM` decimal(10,5) DEFAULT NULL,
  `TimeStamp` timestamp NOT NULL DEFAULT CURRENT_TIMESTAMP ON UPDATE CURRENT_TIMESTAMP,
  PRIMARY KEY (`Id`),
  KEY `CurrencyId` (`CurrencyId`),
  KEY `MetalId` (`MetalId`)
) ENGINE=InnoDB  DEFAULT CHARSET=latin1 COLLATE=latin1_general_ci AUTO_INCREMENT=13 ;

--
-- Dumping data for table `Fixes`
--

INSERT INTO `Fixes` (`Id`, `CurrencyId`, `MetalId`, `FixAM`, `FixPM`, `TimeStamp`) VALUES
(1, 1, 1, '1592.50000', '1586.25000', '2013-02-25 15:10:21'),
(2, 2, 1, '1051.84900', '1049.59300', '2013-02-25 15:10:21'),
(3, 3, 1, '1201.88700', '1194.10600', '2013-02-25 15:10:21'),
(4, 1, 2, '29.17000', NULL, '2013-02-25 13:54:02'),
(5, 2, 2, '19.27580', NULL, '2013-02-25 13:54:02'),
(6, 3, 2, '21.98190', NULL, '2013-02-25 13:54:02'),
(7, 1, 3, '1627.00000', '1620.00000', '2013-02-25 14:28:59'),
(8, 2, 3, '1074.65000', '1072.50000', '2013-02-25 14:28:59'),
(9, 3, 3, '1229.30000', '1218.95000', '2013-02-25 14:28:59'),
(10, 1, 4, '747.00000', '748.00000', '2013-02-25 14:28:59'),
(11, 2, 4, '493.40000', '495.20000', '2013-02-25 14:28:59'),
(12, 3, 4, '564.40000', '562.85000', '2013-02-25 14:28:59');

Answer 1

我想這就是你要找的東西：

SELECT MetalId,
  MAX(CASE WHEN CurrencyId = 1 THEN FixAM END) / 
  MAX(CASE WHEN CurrencyId = 2 THEN FixAM ELSE 1 END) Output
FROM Fixes
GROUP BY MetalId

這產生1592.50000 / 1051.849000。 如果您想要相反，請交換貨幣ID。

SQL小提琴演示

如果您沒有CurrencyId = 2，我將除數值默認為1，這樣您就不會收到錯誤。