mysql 行转列和列转行实例详解

mysql行转列、列转行

 语句不难，不做多余解释了，看语句时，从内往外一句一句剖析

行转列

       有如图所示的表，现在希望查询的结果将行转成列

       建表语句如下：

create table `test_tb_grade` (
 `id` int(10) not null auto_increment,
 `user_name` varchar(20) default null,
 `course` varchar(20) default null,
 `score` float default '0',
 primary key (`id`)
) engine=innodb auto_increment=1 default charset=utf8;

insert into test_tb_grade(user_name, course, score) values
("张三", "数学", 34),
("张三", "语文", 58),
("张三", "英语", 58),
("李四", "数学", 45),
("李四", "语文", 87),
("李四", "英语", 45),
("王五", "数学", 76),
("王五", "语文", 34),
("王五", "英语", 89);

       查询语句：

       此处用之所以用max是为了将无数据的点设为0，防止出现null

select user_name ,
  max(case course when '数学' then score else 0 end ) 数学,
  max(case course when '语文' then score else 0 end ) 语文,
  max(case course when '英语' then score else 0 end ) 英语
from test_tb_grade
group by user_name;

       结果展示：

列转行

       有如图所示的表，现在希望查询的结果将列成行

       建表语句如下：

create table `test_tb_grade2` (
 `id` int(10) not null auto_increment,
 `user_name` varchar(20) default null,
 `cn_score` float default null,
 `math_score` float default null,
 `en_score` float default '0',
 primary key (`id`)
) engine=innodb auto_increment=1 default charset=utf8;

insert into test_tb_grade2(user_name, cn_score, math_score, en_score) values
("张三", 34, 58, 58),
("李四", 45, 87, 45),
("王五", 76, 34, 89);

查询语句：

select user_name, '语文' course , cn_score as score from test_tb_grade2
union select user_name, '数学' course, math_score as score from test_tb_grade2
union select user_name, '英语' course, en_score as score from test_tb_grade2
order by user_name,course;

       结果展示：

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