每个子集的 MAX

And*_*ndy 4 oracle aggregate

我有一张看起来像这样的表:

+---------------------------------------------+
| EVENT_ID | ITEM_ID | PERSON_ID | EVENT_DATE |
+---------------------------------------------+
| 123      | 1       | 2         | 21-AUG-03  |
| 124      | 1       | 3         | 22-AUG-03  |
| 125      | 1       | 45        | 23-AUG-03  |
| 126      | 1       | (null)    | 24-AUG-03  |
| 127      | 2       | 2         | 25-AUG-03  |
| 128      | 2       | 6         | 26-AUG-03  |
| 129      | 2       | 1         | 27-AUG-03  |
+---------------------------------------------+
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因此,我需要获取每个 item_id 的最新 (MAX(event_date)) 非空 person_id。我们为此提出了一个相当简单的 PL/SQL 方法,但试图用直接的 SQL 完成工作。有人有想法吗?

顺便提一下, event_id 并不总是像这样是连续的。我们有两个冗余的数据库服务器。

提前致谢。

Lei*_*fel 7

以下只需要一次全表扫描。

SELECT Item_ID, Person_ID, Event_Date FROM
(
   SELECT Event_ID, Person_ID, Item_ID, Event_Date
      , MAX(EVENT_DATE) OVER (PARTITION BY Item_ID) HighEventDate 
   FROM Event_Table WHERE Person_ID IS NOT NULL
)
WHERE Event_Date = HighEventDate;
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ber*_*d_k 6

尝试这个

create table event_table (
    event_id int,
    item_id int,
    person_id int,
    event_date date
);

insert into event_table values (123, 1, 2,    to_date('21-aug-03','DD-MON-YY'));
insert into event_table values (124, 1, 3,    to_date('22-aug-03','DD-MON-YY')); 
insert into event_table values (125, 1, 45,   to_date('23-aug-03','DD-MON-YY'));  
insert into event_table values (126, 1, null, to_date('24-aug-03','DD-MON-YY'));  
insert into event_table values (127, 2, 2,    to_date('25-aug-03','DD-MON-YY'));  
insert into event_table values (128, 2, 6,    to_date('26-aug-03','DD-MON-YY'));  
insert into event_table values (129, 2, 1,    to_date('27-aug-03','DD-MON-YY'));  


select * from event_table;

select t1.item_id, t1.Person_id, t1.event_date
from event_table t1
join 
(select item_id , max(event_date) max_event_date 
   from event_table where Person_id is not null group by item_id ) t2 
on t1.item_id = t2.item_id and t1.event_date = t2.max_event_date;
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