mysql的行转列以及with rollup求和

create table t_score(
id int primary key auto_increment,
name varchar(20) not null,  #名字
Subject varchar(10) not null, #科目
Fraction double default 0  #分数
);

-- 插入数据
INSERT INTO `t_score`(name,Subject,Fraction) VALUES
         ('王海', '语文', 86),
        ('王海', '数学', 83),
        ('王海', '英语', 93),
        ('陶俊', '语文', 88),
        ('陶俊', '数学', 84),
        ('陶俊', '英语', 94),
        ('刘可', '语文', 80),
        ('刘可', '数学', 86),
        ('刘可', '英语', 88),
        ('李春', '语文', 89),
        ('李春', '数学', 80),
        ('李春', '英语', 87);

方法一、if

select name as 名字 ,
sum(if(Subject='语文',Fraction,0)) as 语文,
sum(if(Subject='数学',Fraction,0))as 数学, 
sum(if(Subject='英语',Fraction,0))as 英语,
round(AVG(Fraction),2) as 平均分,
SUM(Fraction) as 总分
from t_score group by name     
union
select name as 名字 , sum(语文) Chinese,sum(数学) Math,sum(英语) English,round(AVG(总分),2)as 平均分,sum(总分) score  from(
select 'TOTAL' as name,
sum(if(Subject='语文',Fraction,0)) as 语文,
sum(if(Subject='数学',Fraction,0))as 数学, 
sum(if(Subject='英语',Fraction,0))as 英语,
SUM(Fraction) as 总分
from t_score group by Subject )t

上面简单的语句更新了我以往的写sql的习惯

-- oracle语法

select name as 名字 ,
sum(case when subject='语文'  then score else '0' end)  语文，
sum(case when subject='数学'  then score else '0' end)  数学，
sum(case when subject='英语'  then score else '0' end)  英语,
round(AVG(score),2) as 平均分,
sum(score)/count(*) ,
SUM(score) as 总分
from lagfunction group by name 



-- 2.0在oracle中自己常用的习惯
select name ,sum(A),sum(B),sum(C) ，（sum(A)+sum(B)+sum(C) ）/count(*) from (
select NAME ,SCORE AS A,0 AS B,0 AS c 

from lagfunction   WHERE subject='语文' 
union 
select NAME ,0 AS A,SCORE AS B,0 AS c 

from lagfunction   WHERE subject='数学'
union 
select NAME ,0 AS A,0 AS B,SCORE AS c 

from lagfunction   WHERE subject='英语' )c  GROUP BY NAME

发现自己以往写作习惯真是太基础了，

方法二、case

select  name as Name,
sum(case when Subject = '语文' then Fraction end) as Chinese,
sum(case when Subject = '数学' then Fraction end) as Math,
sum(case when Subject = '英语' then Fraction end) as English,
sum(fraction)as score
from t_score group by name
UNION ALL
select  name as Name,sum(Chinese) as Chinese,sum(Math) as Math,sum(English) as English,sum(score) as score from(
select 'TOTAL' as name,
sum(case when Subject = '语文' then Fraction end) as Chinese,
sum(case when Subject = '数学' then Fraction end) as Math,
sum(case when Subject = '英语' then Fraction end) as English,
sum(fraction)as score
from t_score group by Subject)t

方法三、使用with rollup

select 
        ifnull(name,'TOll') name,
        sum(if(Subject='语文',Fraction,0)) as 语文,
       sum(if(Subject='英语',Fraction,0)) as 英语,
       sum(if(Subject='数学',Fraction,0))as 数学,
       sum(Fraction) 总分
        from t_score group by name with rollup

◆with rollup的作用是在最下面加上一行总的求和，看下图，当涉及到avg的时候，该函数智能的求了个总的平均，有意思！

参考：https://www.cnblogs.com/weibanggang/p/9679301.html