Oracle检索最大记录

Question

Table_A
A_id          
1     

Tale_B
B_id       A_id
1            1
2            1
3            1
Table_C
B_id      Process_date
1   20130101 12:20:01
2   20130101 12:10:01
3   20130101 13:00:01

如何从Table_C中获取最大的process_date，并基于Table_C计时窗口引用Table_A a__id。如果我想在定时窗口20130101 12:09:00到12:21:00中检索Table_C id和max(process_date)，那么它应该返回id为1,process_date为12:20:01

Answer 1

您可以使用获取max(process_date):

的子查询。

select c1.b_id,
  c2.MaxDate
from table_a a
inner join table_b b
  on a.a_id = b.a_id
inner join table_c c1
  on b.b_id = c1.b_id
inner join
(
  select max(process_date) MaxDate
  from table_c
) c2
  on c1.process_date = c2.maxdate;

参见SQL Fiddle with Demo

或者您可以使用row_number():

select b_id, process_date
from 
(
  select c1.b_id,
    c1.process_date,
    row_number() over(partition by a.a_id order by c1.process_date desc) rn
  from table_a a
  inner join table_b b
    on a.a_id = b.a_id
  inner join table_c c1
    on b.b_id = c1.b_id
) 
where rn = 1

参见SQL Fiddle with Demo

Answer 2

这个查询应该得到每个Table_A中引用的B_id的最大process_date:

SELECT c.B_id, MAX(Process_date)
FROM Table_C c
INNER JOIN Table_B b 
    ON b.B_id = c.B_id
INNER JOIN Table_A a
    ON a.A_ID = b.A_id
GROUP BY c.B_id

只要从选择中删除c.B_id和GROUP BY，如果你想要所有B_id的最大process_date与Table_A的引用。

SQL小提琴