Question

我在任务和操作之间有关系。我想在没有操作的情况下选择手动任务，或者选择一个动作！='取消'进行上一次操作。

实施例

tasks table :
-------------
|id | state |
| 3 |auto   |
| 5 |manual |
| 6 |manual |
| 2 |manual |
| 8 |manual |

operations table :
----------------------------------
|id | action    | task_id | time |
| 1 | processed | 8       | 8:00 |
| 2 | cancelled | 8       | 9:00 |
| 3 | processed | 6       | 8:00 |
| 4 | processed | 2       | 8:00 |
| 5 | cancelled | 2       | 7:00 |

result : tasks 5,6,2

以下是我设法做的事情：

SELECT tasks.*
WHERE tasks.id NOT IN(
    SELECT operations.task_id)
OR tasks.id IN
    SELECT operations.task_id
    WHERE action!=cancelled
    .....
    .....
    ORDER BY time DESC

我不确定如何结束此查询。此外，它还将对任务中的每一行执行2次查询。

Answer 1

嗯。我在想distinct on获取有关操作的信息：

select distinct on (task_id)
from operations o
order by task_id, time desc;

然后left join来完成任务：

select t.*
from tasks t left join
     (select distinct on (task_id)
      from operations o
      order by task_id, time desc
     ) o
     on o.task_id = t.task_id
where o.task_id is null or o.action <> 'cancelled';

Answer 2

让我们说这是你的架构：

CREATE TABLE tasks (
    id int unique,
    state text
);

CREATE TABLE operations (
    id serial,
    action text,
    task_id int REFERENCES tasks (id),
    time text
);

INSERT INTO tasks (id, state) VALUES (3, 'auto');
INSERT INTO tasks (id, state) VALUES (5, 'manual');
INSERT INTO tasks (id, state) VALUES (6, 'manual');
INSERT INTO tasks (id, state) VALUES (2, 'manual');
INSERT INTO tasks (id, state) VALUES (8, 'manual');

INSERT INTO operations (action, task_id, time) VALUES ('processed', 8, '8:00');
INSERT INTO operations (action, task_id, time) VALUES ('cancelled', 8, '9:00');
INSERT INTO operations (action, task_id, time) VALUES ('processed', 6, '8:00');
INSERT INTO operations (action, task_id, time) VALUES ('processed', 2, '8:00');
INSERT INTO operations (action, task_id, time) VALUES ('cancelled', 2, '7:00');

这将是您的查询：

SELECT *
FROM tasks
WHERE state = 'manual' AND
      (
        NOT EXISTS (SELECT 1 FROM operations WHERE task_id = tasks.id LIMIT 1)
        OR
        (SELECT action FROM operations WHERE task_id = tasks.id ORDER BY id DESC LIMIT 1) != 'cancelled'
      )
;

输出：

 id | state  
----+--------
  5 | manual
  6 | manual
(2 rows)

Answer 3

如果您愿意依赖＆＃39;取消＆＃39;是任务执行的最后一次操作 - 即，如果取消将任务置于终端状态，那么就不必专注于取消 last 操作，只取决于是否取消。

在这种情况下，您可以使用相当简单的外部联接来查找结果：

select t.*
from
  tasks t
  left outer join operations o
    on t.id = o.task_id
       and o.action = 'cancelled'
where t.state = 'manual' and o.id is null;

特别注意过滤条件中的o.id is null - 假设＆＃39; id＆＃39;表是operations的主键，只有在operations的行不满足tasks的给定行的连接条件时，它才能在连接结果中为空。也就是说，仅适用于没有关联＆＃39;取消＆＃39;操作（包括那些根本没有操作的操作）。

另一方面，如果您需要包含已取消＆＃39;操作，但 last 操作不同，那么您可以使用窗口函数来帮助您识别每个任务的最后一个操作：

select t.*
from
  tasks t
  left outer join (
      select
        operations.*,
        max(operations.time) over (partition by task_id) as last_time 
      from operations
    ) o
    on t.id = o.task_id
      and o.action = 'cancelled'
      and o.time = o.last_time
where t.state = 'manual' and o.id is null;

此处必须o.time = o.last_time出现在连接条件中，而不是内联视图的过滤条件（它将是非法的）或外部查询的过滤条件（它将出错的地方）效果）。

按最后关系选择或没有关系

3 个答案: