如何在时间查询中进行左连接

Question

我有以下 table:

char, id_1, id_2
a,100,50
a,100,50
a,100,50
b,101,50
b,101,50
c,200,51
c,200,51
d,201,51
e,202,52
e,202,52
e,202,52
e,202,52

我想产生这个输出：

id_1, id_2, count, sum
100,50,3,5
101,50,2,5
200,51,2,3
201,51,1,3
202,52,4,4

简短说明：

我想计算给定“id_1”的行数并生成列“count” 然后一旦我有了“计数”列，我想通过对组求和来创建“总和”列 id_2

我先试试这个：

select id_1, id_2, count(id_2) as count from myTable
group by id_1, id_2

制作计数列，

id_1, id_2, count
100,50,3
101,50,2
200,51,2
201,51,1
202,52,4

问题是我无法创建总和列。

你有什么想法吗？提前致谢。

Answer 1

如果您使用的是 MySql 8+，那么 window 函数 让这变得相对简单：

select id_1, id_2, Count(*) "Count", Max(cnt) "sum"
from (
    select *, Count(*) over(partition by id_2) cnt
    from t
)t
group by id_1, id_2;

See demo Fiddle

Answer 2

正如 Stu 所说，window 函数使这项任务变得轻而易举。这是我对这项任务的看法（当我完成时，Stu 已经回复了，无论如何也可以分享我的）。

架构 (MySQL v8.0)

CREATE TABLE Test (
  `id_1` INTEGER,
  `id_2` INTEGER
);

INSERT INTO Test
  (`id_1`, `id_2`)
VALUES
  ('100', '50'),
  ('100', '50'),
  ('100', '50'),
  ('101', '50'),
  ('101', '50'),
  ('200', '51'),
  ('200', '51'),
  ('201', '51'),
  ('202', '52'),
  ('202', '52'),
  ('202', '52'),
  ('202', '52');

查询#1

select distinct 
*,
count(id_1) over (partition by id_1) as count,
count(id_2) over (partition by id_2) as sum
from Test;

id_1	id_2	count	sum
100	50	3	5
101	50	2	5
200	51	2	3
201	51	1	3
202	52	4	4

View on DB Fiddle

如何在时间查询中进行左连接

How can I make a left join in a temporal query

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