[Transfer] About converting column values to column names in MySQL

We sometimes have this need:

This kind of display related to column values ​​is sometimes very intuitive to the data. I will use a small demo to realize this kind of operation.

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Table Structure

create table demo1(
    sname  varchar(20) not null  comment '学员',
    course varchar(10) not  null comment '科目',
    score float    not null comment '成绩'
)

Insert the following data:

takes off	course	score
Zhang San	language	100
Zhang San	math	90
Zhang San	English	80
Li Si	language	90
Li Si	math	70
Li Si	English	100

MySQL provides conditional branch syntax (similar to if/else, case...)

Syntax:
1.case key when condition then result when condition then result...else key (the default is original) end
2.if(field as column = 'value', data field to be displayed, another value)

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Above code:

select sname '姓名',
max(if(course = '语文', score,0))  '语文',
avg(case course when '数学' then score end)  '数学',
max(if(course = '英语',score,0))  '英语' 
from demo1 group by sname;

Results of the:

 Reprint address: https://www.cnblogs.com/wxxwjef/p/14952252.html

A sql reference written by myself

select col1,,col2  ,
MAX(if(region_type='frontier',first_prop,'')) col3,
MAX(if(region_type='finepublic',first_prop,'')) col4,
MAX(if(region_type='cn_finepublic',first_prop,'')) col5,
MAX(if(region_type='importantinst',first_prop,'')) col6,
MAX(if(region_type='leadings',first_prop,'')) col7
from 
(select  b.name as col1,b.name_abbr as col2 , a.* 
from 
(select subject_id,region_type,group_concat(first_prop) as first_prop from search_expression_list where region_type!='keyword' group by subject_id,region_type) as a
join subject_info b
on  a.subject_id = b.id
)as c 
group by col2