sql - 计算oracle中两个日期之间每小时的记录数

Question

我需要一个在 oracle 中执行此序列的 SINGLE 查询。

select count(*) from table1
where request_time < timestamp'2012-05-19 12:00:00' and (end_time > timestamp'2012-05-19 12:00:00' or end_time=null);

select count(*) from table1
where request_time < timestamp'2012-05-19 13:00:00' and (end_time > timestamp'2012-05-19 13:00:00' or end_time=null);

select count(*) from table1
where request_time < timestamp'2012-05-19 14:00:00' and (end_time > timestamp'2012-05-19 14:00:00' or end_time=null);

select count(*) table1
where request_time < timestamp'2012-05-19 15:00:00' and (end_time > timestamp'2012-05-19 15:00:00' or end_time=null);

select count(*) from table1
where request_time < timestamp'2012-05-19 16:00:00' and (end_time > timestamp'2012-05-19 16:00:00' or end_time=null);

如您所见，小时正在一点一点地增加。
这是输出

COUNT(*)               
1085                   

COUNT(*)               
1233                   

COUNT(*)               
1407                   

COUNT(*)               
1322                   

COUNT(*)               
1237

我写了一个查询，但它没有给我正确的答案!

select col1, count(*) from
(select TO_CHAR(request_time, 'YYYY-MM-DD HH24') as col1 from table1
 where request_time <= timestamp'2012-05-19 12:00:00' and (end_time >= timestamp'2012-05-19 12:00:00' or end_time=null))
group by col1 order by col1;

这个查询给了我一个结果集，它的 count(*) 的总和等于上面写的第一个查询!
结果如下:

COL1          COUNT(*)               
------------- ---------------------- 
2012-05-19 07      22                     
2012-05-19 08      141                    
2012-05-19 09      322                    
2012-05-19 10      318                    
2012-05-19 11      282  

Answer 1

注意trunc的用法带有日期值的表达式。您可以省略 alter session如果您没有在 sql*plus 中运行查询。

SQL> alter session set nls_date_format='yyyy-mm-dd hh24:mi:ss';

Session altered.

SQL> SELECT 
       trunc(created,'HH'), 
       count(*) 
     FROM 
       test_table 
     WHERE 
       created > trunc(SYSDATE -2) 
     group by trunc(created,'HH');


TRUNC(CREATED,'HH')   COUNT(*)
------------------- ----------
2012-05-21 09:00:00        748
2012-05-21 16:00:00         24
2012-05-21 17:00:00         12
2012-05-21 22:00:00        737
2012-05-21 23:00:00        182
2012-05-22 20:00:00         16
2012-05-22 21:00:00        293
2012-05-22 22:00:00        610

8 ROWS selected.