sql分組 case條件查詢

1.首先建表，插入數據
DROP TABLE IF EXISTS `aa`;
CREATE TABLE `aa` (
  `id` int(255) NOT NULL AUTO_INCREMENT,
  `user` varchar(255) DEFAULT NULL,
  `year` varchar(255) DEFAULT NULL,
  `month` varchar(255) DEFAULT NULL,
  `payment` varchar(255) DEFAULT NULL,
  PRIMARY KEY (`id`)
) ENGINE=InnoDB AUTO_INCREMENT=8 DEFAULT CHARSET=utf8;

INSERT INTO `aa` VALUES ('1', 'A', '2018', '1', '1.1');
INSERT INTO `aa` VALUES ('2', 'A', '2018', '1', '1.0');
INSERT INTO `aa` VALUES ('3', 'A', '2018', '2', '1.2');
INSERT INTO `aa` VALUES ('4', 'A', '2018', '3', '1.3');
INSERT INTO `aa` VALUES ('5', 'B', '2018', '1', '1.4');
INSERT INTO `aa` VALUES ('6', 'B', '2018', '2', '1.5');
INSERT INTO `aa` VALUES ('7', 'B', '2018', '3', '1.6');

2.按照user,month分組查詢，並計算payment合計
SELECT user,year,
SUM(CASE WHEN month = 1 THEN payment ELSE 0 END) as month1,
SUM(CASE WHEN month = 2 THEN payment ELSE 0 END) as month2,
SUM(CASE WHEN month = 3 THEN payment ELSE 0 END) as month3,
SUM(payment) total
FROM aa GROUP BY user;