mysql 多行变一行 若行与列转换
2008-10-16 09:42 345人阅读 评论(0) 收藏 举报
DateClass Class Count
2004-02 AU 32
2004-02 VAIO 56
2004-02 PB 77
2004-02 TV 89
2004-03 AU 38
2004-03 VAIO 99
2004-03 PB 32
2004-03 TV 87
要将查询结果变为
DateClass AU VAIO PB TV
2004-02 32 56 77 89
2004-03 38 99 32 87
建表：
CREATE TABLE `test` (
`dataClass` varchar(25) DEFAULT NULL,
`class` varchar(25) DEFAULT NULL,
`count` varchar(25) DEFAULT NULL
);
-- ----------------------------
-- Records
-- ----------------------------
INSERT INTO `test` VALUES ('2004-02', 'AU', '32');
INSERT INTO `test` VALUES ('2004-02', 'VAIO', '56');
INSERT INTO `test` VALUES ('2004-03', 'AU', '38');
INSERT INTO `test` VALUES ('2004-03', 'PB', '55');
ＳＱＬ实现：
select DataClass ,
max(case when class = 'AU' then Count else 0 end) as AU,
max(case when class = 'VAIO' then Count else 0 end) as VAIO,
max(case when class = 'PB' then Count else 0 end) as PB,
max(case when class = 'TV' then Count else 0 end) as TV
from test
group by DataClass;
结果：
+-----------+----+------+----+----+
| DataClass | AU | VAIO | PB | TV |
+-----------+----+------+----+----+
| 2004-02 | 32 | 56 | 0 | 0 |
| 2004-03 | 38 | 0 | 55 | 0 |
+-----------+----+------+----+----+
2 rows in set