sql - oracle:按日期和时间戳排序

Question

我使用union从三个表中选择一些数据，然后按日期和时间戳（降序）对它们进行排序：

select reportname as name, convert_to_char(a.date) AS created,
....
from table1 

UNION
select reportname as name, convert_to_char(a.date) AS created,
....
from table2

UNION
select reportname as name, convert_to_char(a.date) AS created,
....
from table3

order by created desc;

convert_to_char的实现如下：

create or replace function convert_to_char(myDate date) 
RETURN varchar IS
BEGIN
return TO_CHAR(cast (myDate as timestamp) at local, 'YYYY-MM-DD HH24:MI:SS TZH:TZM');
END;

我得到的排序数据的结果如下所示：

created
------------------
2017-04-12 16:07:07 +02:00
2017-04-13 09:00:01 +02:00
2017-04-13 09:00:40 +02:00
2017-04-12 16:06:17 +02:00
2017-04-12 16:08:37 +02:00
2017-04-12 16:07:31 +02:00
2017-04-13 09:00:25 +02:00
2017-04-13 09:00:25 +02:00
2017-04-12 16:09:07 +02:00
2017-04-12 16:08:20 +02:00
2017-04-12 16:08:06 +02:00
2017-04-12 16:06:48 +02:00

但我期望以下排序结果：

created
------------------
2017-04-13 09:00:40 +02:00
2017-04-13 09:00:25 +02:00
2017-04-13 09:00:25 +02:00
2017-04-13 09:00:01 +02:00
2017-04-12 16:09:07 +02:00
2017-04-12 16:08:37 +02:00
2017-04-12 16:08:20 +02:00
2017-04-12 16:08:06 +02:00
2017-04-12 16:07:31 +02:00
2017-04-12 16:07:07 +02:00
2017-04-12 16:06:48 +02:00
2017-04-12 16:06:17 +02:00

任何想法如何获得预期的排序结果？

先感谢您。

Answer 1

您可以先对它们进行排序，然后选择

select name, created 
from 
(select reportname as name, convert_to_char(a.date) AS created, a.date,
 ....
from table1 

UNION
select reportname as name, convert_to_char(a.date) AS created, a.date
....
from table2

UNION
select reportname as name, convert_to_char(a.date) AS created, a.date
....
from table3
order by a.date desc);