题目1：实现如下效果
1 CREATE TABLE IF NOT EXISTS tb_amount( 2 `Id` INT NOT NULL AUTO_INCREMENT, 3 `Year` CHAR(4), 4 `Month` CHAR(2), 5 `Amount` DECIMAL(5,2), 6 PRIMARY KEY(`Id`) 7 ); 8 9 INSERT INTO `tb_amount`(`Year`, `Month`, `Amount`) VALUES('1991', '1', '1.1'); 10 INSERT INTO `tb_amount`(`Year`, `Month`, `Amount`) VALUES('1991', '2', '1.2'); 11 INSERT INTO `tb_amount`(`Year`, `Month`, `Amount`) VALUES('1991', '3', '1.3'); 12 INSERT INTO `tb_amount`(`Year`, `Month`, `Amount`) VALUES('1991', '4', '1.4'); 13 INSERT INTO `tb_amount`(`Year`, `Month`, `Amount`) VALUES('1992', '1', '2.1'); 14 INSERT INTO `tb_amount`(`Year`, `Month`, `Amount`) VALUES('1992', '2', '2.2'); 15 INSERT INTO `tb_amount`(`Year`, `Month`, `Amount`) VALUES('1992', '3', '2.3'); 16 INSERT INTO `tb_amount`(`Year`, `Month`, `Amount`) VALUES('1992', '4', '2.4'); 17 18 SELECT `Year`, 19 (SELECT Amount FROM tb_amount m WHERE `Month`=1 AND m.`Year`=tb_amount.`Year`) AS m1, 20 (SELECT Amount FROM tb_amount m WHERE `Month`=2 AND m.`Year`=tb_amount.`Year`) AS m2, 21 (SELECT Amount FROM tb_amount m WHERE `Month`=3 AND m.`Year`=tb_amount.`Year`) AS m3, 22 (SELECT Amount FROM tb_amount m WHERE `Month`=4 AND m.`Year`=tb_amount.`Year`) AS m4 23 FROM tb_amount GROUP BY `Year`;