mysql行转列问题 SUM(IF(条件,列值,0))

sum(if(条件,列值,0))语法用例：

select name,sum(if(subject="语文",score,0)) as “语文” from grade GROUP BY name

if中第一个参数为条件，符合条件的内容才会将第二个参数相加，不符合的内容将第三个参数相加。

第二个参数为要相加的参数，可以用常量，也可以用字段值。

第三个参数为条件为假时相加的值，通常设为0.

为了将行转为列（这种操作一般用于统计），可使用如下语句：

select name,sum(if(subject="语文",score,0)) as “语文”,

sum(if(subject="数学",score,0)) as “数学”,sum(if(subject="英语",score,0)) as “英语”

from grade GROUP BY name

结果

mysql行列转换

创建数据库、表

create database tests;
use tests;
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
);

添加数据

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);

方式一:使用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

方式二:使用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: 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