技術標籤：筆記MySQL

題目來源：https://www.jianshu.com/p/0f165dcf9525

目錄

• 第3題
• • 1.1 題目（行轉列）
  • 1.2 解題
• 第4題
• • 2.1 題目（列轉行）
  • 2.2 解題

第3題

1.1 題目（行轉列）

建表語句：

-- 建立 course 表
create table course (
id varchar(20),
teacher_id varchar(20),
week_day varchar(20),
has_course varchar(20)
);
insert into course value
(1,1,2,"Yes"),
(
 
2,1,3,"Yes"),
(3,2,1,"Yes"),
(4,3,2,"Yes"),
(5,1,2,"Yes");

1.2 解題

select teacher_id,
       (case when week_day='1' then 'YES' else '' end) as 'mon',
       (case when week_day='2' then 'YES' else '' end) as 'tue',
       (case when week_day='3' then 'YES' else
 
 '' end) as 'thi',
       (case when week_day='4' then 'YES' else '' end) as 'thu',
       (case when week_day='5' then 'YES' else '' end) as 'fri'
from course;

第4題

2.1 題目（列轉行）

建表語句：

create table a1 (
name varchar(20),
english int,
maths int,
music int);

insert into a1 values
("Jim",90,88
 
,99);

2.2 解題

select name, 'english' as subject, english as score from a1
union all
select name, 'maths' as subject, maths as score from a1
union all
select name, 'music' as subject, music as score from a1
order by name;