如何把mysql的列修改成行显示数据简单实现

创建测试表：

   1: DROP TABLE IF EXISTS `test`;

   2: CREATE TABLE `test` (

   3:   `year` int(11) DEFAULT NULL,

   4:   `month` int(11) DEFAULT NULL,

   5:   `amount` double DEFAULT NULL

   6: ) ENGINE=InnoDB DEFAULT CHARSET=utf8;

插入数据：

   1: INSERT INTO `test` VALUES (‘1991‘, ‘1‘, ‘1.1‘);

   2: INSERT INTO `test` VALUES (‘1991‘, ‘2‘, ‘1.2‘);

   3: INSERT INTO `test` VALUES (‘1991‘, ‘3‘, ‘1.3‘);

   4: INSERT INTO `test` VALUES (‘1991‘, ‘4‘, ‘1.4‘);

   5: INSERT INTO `test` VALUES (‘1992‘, ‘1‘, ‘2.1‘);

   6: INSERT INTO `test` VALUES (‘1992‘, ‘2‘, ‘2.2‘);

   7: INSERT INTO `test` VALUES (‘1992‘, ‘3‘, ‘2.3‘);

   8: INSERT INTO `test` VALUES (‘1992‘, ‘4‘, ‘2.3‘);

看到题目要求，仔细想想可以：

利用SUM(IF()) 生成列 + WITH ROLLUP 生成汇总行,并利用 IFNULL将汇总行标题显示为 Total_num

实现
SQL代码块如下：

   1: select year,

   2:     sum(if(month=1,amount,0)) as "M1",

   3:     sum(if(month=2,amount,0)) as "M2",

   4:     sum(if(month=3,amount,0)) as "M3",

   5:     sum(if(month=4,amount,0)) as "M4"

   6: from test

   7: GROUP by year;

效果如下：