191、统计每年每月的信息

johnny

191、统计每年每月的信息

year  month amount
1991   1     1.1
1991   2     1.2
1991   3     1.3
1991   4     1.4
1992   1     2.1
1992   2     2.2
1992   3     2.3
1992   4     2.4
查成这样一个结果
year m1  m2  m3  m4
1991 1.1 1.2 1.3 1.4
1992 2.1 2.2 2.3 2.4

提示：这个与工资条非常类似，与学生的科目成绩也很相似。

 

准备sql语句：

drop table if exists sales;

create table sales(id int auto_increment primary key,year varchar(10), month varchar(10), amount float(2,1));

insert into sales values

(null,'1991','1',1.1),

(null,'1991','2',1.2),

(null,'1991','3',1.3),

(null,'1991','4',1.4),

(null,'1992','1',2.1),

(null,'1992','2',2.2),

(null,'1992','3',2.3),

(null,'1992','4',2.4);
答案一、
select sales.year ,

(select t.amount from sales t where t.month='1' and t.year= sales.year) '1',

(select t.amount from sales t where t.month='1' and t.year= sales.year) '2',

(select t.amount from sales t where t.month='1' and t.year= sales.year) '3',

(select t.amount from sales t where t.month='1' and t.year= sales.year) as '4'

from sales  group by year;

chu@

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