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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