PostgreSQL 分组

Question

我想根据多列中的值对值进行分组。 这是一个例子:

我想得到输出:

{{-30,-50,20},{-20,30,60},{-30,NULL or other value, 20}}

我设法到达:

SELECT array_agg("val") 
FROM my_table 
WHERE "t_id" = 1  
GROUP BY "m_id";

{{-30,-50,20},{-20,30,60},{-30,20}}

什么是最好的方法？

Answer 1

create table my_table (
    t_id int,
    m_id int,
    s_id int,
    val int
);
insert into my_table (t_id, m_id, s_id, val) values
(1,1,1,-30),
(1,1,2,-50),
(1,1,3,20),
(1,2,1,-20),
(1,2,2,30),
(1,2,3,60),
(1,3,1,-30),
(1,3,3,20);

---

select array_agg(val order by s_id) 
from
    my_table t
    right join
    (
        (
            select distinct t_id, m_id
            from my_table
        ) a
        cross join
        (
            select distinct s_id
            from my_table
        ) b
    ) s using (t_id, m_id, s_id)
where t_id = 1  
group by m_id
order by m_id
;
   array_agg   
---------------
 {-30,-50,20}
 {-20,30,60}
 {-30,NULL,20}