mysql 查询小demo

 

 

两张表的的结构如下，需求是写出从one表到two表和从two表到one表的查询转换。

create table student_one(
	name varchar(50) default '' not null,
	type varchar(10) not null default 0,
	score float(5,2) not null default 0.00
)Engine=innodb;


create table student_two(
	name varchar(50) default '' not null,
	math  float(5,2) not null default 0.00,
	english float(5,2) not null default 0.00,
	chinese float(5,2) not null default 0.00
)Engine=innodb;

　　目前表中数据如下所示

 

以表one为基准查出表two的格式的语句如下：

select a.name,a.score as 'math',b.score as 'chinese',c.score as 'english'
from student_one a join student_one b join student_one c 
on a.name=b.name and a.name=c.name and b.name=c.name 
where a.type='math' and b.type='chinese' and c.type='Engine';

查询结果如下图所示：

　　

 

 

以表two为基准查出表one的格式的语句如下：

select a.name,a.math as score,'math' as type from student_two a 
union
select b.name,b.english as score,'english' as type from student_two b 
union
select c.name,c.chinese as score,'chinese' as type from student_two c;

　　查询结果如下：

 

来源：https://www.cnblogs.com/ddddemo/p/6637427.html