mysql 经典题目

题目1：实现如下效果

 CREATE TABLE IF NOT EXISTS tb_amount(
    `Id` INT NOT NULL AUTO_INCREMENT,
    `Year` CHAR(4),
    `Month` CHAR(2),
    `Amount` DECIMAL(5,2),
    PRIMARY KEY(`Id`)
 );

 INSERT INTO `tb_amount`(`Year`, `Month`, `Amount`) VALUES('', '', '1.1');
 INSERT INTO `tb_amount`(`Year`, `Month`, `Amount`) VALUES('', '', '1.2');
 INSERT INTO `tb_amount`(`Year`, `Month`, `Amount`) VALUES('', '', '1.3');
 INSERT INTO `tb_amount`(`Year`, `Month`, `Amount`) VALUES('', '', '1.4');
 INSERT INTO `tb_amount`(`Year`, `Month`, `Amount`) VALUES('', '', '2.1');
 INSERT INTO `tb_amount`(`Year`, `Month`, `Amount`) VALUES('', '', '2.2');
 INSERT INTO `tb_amount`(`Year`, `Month`, `Amount`) VALUES('', '', '2.3');
 INSERT INTO `tb_amount`(`Year`, `Month`, `Amount`) VALUES('', '', '2.4');

 SELECT `Year`,
 (SELECT Amount FROM   tb_amount m WHERE `Month`=1   AND m.`Year`=tb_amount.`Year`) AS m1,
 (SELECT Amount FROM   tb_amount m WHERE `Month`=2   AND m.`Year`=tb_amount.`Year`) AS m2,
 (SELECT Amount FROM   tb_amount m WHERE `Month`=3   AND m.`Year`=tb_amount.`Year`) AS m3,
 (SELECT Amount FROM   tb_amount m WHERE `Month`=4   AND m.`Year`=tb_amount.`Year`) AS m4
 FROM tb_amount  GROUP BY `Year`;