MySQL根据条件进行计数和求和 [英] MySQL Count and sum based on condition

问题描述

是否有一种方法可以为每个PN计数SN并根据条件(在以下情况下为Loc)对它进行求和?

Is there a way to count SN for each PN and sum it based on a condition (in below case Loc)?

create table table1 (
            code int(10) primary key,
            PN varchar(10) not null,
        SN varchar(10) not null,
                Loc varchar(10));

insert into table1 values (1,'T1','a1','a');
insert into table1 values (2,'T1','a2','a');
insert into table1 values (3,'T1','a3','a');
insert into table1 values (4,'T1','a4','b');
insert into table1 values (5,'T1','a5','b');
insert into table1 values (6,'T1','a6','b');
insert into table1 values (7,'T2','a1','a');
insert into table1 values (8,'T2','a2','a');
insert into table1 values (9,'T2','a3','a');
insert into table1 values (10,'T2','a4','b');
insert into table1 values (11,'T2','a5','b');
insert into table1 values (12,'T2','a6','b');
insert into table1 values (13,'T2','a7','b');

我试图达到的结果是:

PN  a   b
T1  3   3
T2  3   4

推荐答案

这只是条件聚合:

select pn, sum(loc = 'a') as a, sum(loc = 'b') as b
from table1
group by pn;

如果您有loc值的未知列表，则可能需要动态查询. Google"MySQL动态枢纽".

If you have an unknown list of loc values, then you might need a dynamic query. Google "MySQL dynamic pivot".

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