Postgresql - 在列具有重复值的行中增加计数器

Question

我在用于调度的表中添加了一个列 (seq)，以便前端可以管理每个项目的显示顺序。是否可以制作一个 SQL 查询来根据日期列中的常见重复值使用增量计数器填充此列？

之前

------------------------------------
| name | date_time           | seq |
------------------------------------
| ABC1 | 15-01-2017 11:00:00 |     |
| ABC2 | 16-01-2017 11:30:00 |     |
| ABC1 | 16-01-2017 11:30:00 |     |
| ABC3 | 17-01-2017 10:00:00 |     |
| ABC3 | 18-01-2017 12:30:00 |     |
| ABC4 | 18-01-2017 12:30:00 |     |
| ABC1 | 18-01-2017 12:30:00 |     |
------------------------------------  

之后

------------------------------------
| name | date_time           | seq |
------------------------------------
| ABC1 | 15-01-2017 11:00:00 | 0   |
| ABC2 | 16-01-2017 11:30:00 | 0   |
| ABC1 | 16-01-2017 11:30:00 | 1   |
| ABC3 | 17-01-2017 10:00:00 | 0   |
| ABC3 | 18-01-2017 12:30:00 | 0   |
| ABC4 | 18-01-2017 12:30:00 | 1   |
| ABC1 | 18-01-2017 12:30:00 | 2   |
------------------------------------

已解决，感谢两个答案。 为了让任何发现这个的人更容易，工作代码是：

UPDATE my_table f
    SET seq = seq2
    FROM (
        SELECT ctid, ROW_NUMBER() OVER (PARTITION BY date_time ORDER BY ctid) -1 AS seq2
        FROM my_table
        ) s
    WHERE f.ctid = s.ctid;

Answer 1

使用window functionrow_number()：

with my_table (name, date_time) as (
values

('ABC1', '15-01-2017 11:00:00'),
('ABC2', '16-01-2017 11:30:00'),
('ABC1', '16-01-2017 11:30:00'),
('ABC3', '17-01-2017 10:00:00'),
('ABC3', '18-01-2017 12:30:00'),
('ABC4', '18-01-2017 12:30:00'),
('ABC1', '18-01-2017 12:30:00')
)

select *, 
    row_number() over (partition by name order by date_time)- 1 as seq
from my_table
order by date_time;

 name |      date_time      | seq 
------+---------------------+-----
 ABC1 | 15-01-2017 11:00:00 |   0
 ABC1 | 16-01-2017 11:30:00 |   1
 ABC2 | 16-01-2017 11:30:00 |   0
 ABC3 | 17-01-2017 10:00:00 |   0
 ABC1 | 18-01-2017 12:30:00 |   2
 ABC3 | 18-01-2017 12:30:00 |   1
 ABC4 | 18-01-2017 12:30:00 |   0
(7 rows)

阅读this answer 了解有关使用唯一整数更新现有记录的类似问题。

Answer 2

查看ROW_NUMBER()。

SELECT name, date_time, ROW_NUMBER() OVER (PARTITION BY date_time ORDER BY name) FROM [table]