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中检索基于Table_C时间窗口的Table_A A_id的最大process_date。如果我想在时间窗口20130101 12:09:00到12:21:00检索Table_C id和max（process_date），那么它应该将id返回为1，将process_date返回为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;

请参阅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

请参阅SQL Fiddle with Demo

Answer 2

此查询应该为process_date中的每个B_id提供Table_A的最大值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：

c.B_id

如果您希望所有B_id的最大GROUP BY引用process_date，请从选择中删除Table_A，{{1}}。

SQL Fiddle

Oracle检索最大记录

2 个答案: