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`;