Question

我在表格中有两个时间戳：

     usage_from      |     usage_till     
---------------------+--------------------
 2013-10-09 23:08:17 | 2013-10-09 23:16:00
 2013-10-09 23:08:17 | 2013-10-09 23:08:19
 2013-10-09 23:08:17 | 2013-10-10 18:58:22
 2013-10-09 23:08:17 | 2013-10-09 23:15:05
 2013-10-09 23:08:17 | 2013-10-09 23:09:00
 2013-10-09 23:08:17 | 2013-10-09 23:08:20
 2013-10-09 23:08:17 | 2013-10-09 23:32:04
 2013-10-09 23:08:17 | 2013-10-10 02:02:03
 2013-10-09 23:08:17 | 2013-10-10 07:31:00
 2013-10-09 23:08:17 | 2013-10-10 22:41:04

我需要分成如下：

 usage_from      |     usage_till        
---------------------+-----------------------
 2013-10-09 23:08:17 |  2013-10-09 23:16:00 
 2013-10-09 23:08:17 |  2013-10-09 23:08:19 
 2013-10-09 23:08:17 |  2013-10-10 02:00:00 
 2013-10-10 02:00:00 |  2013-10-10 18:58:22 -- splitted
 2013-10-09 23:08:17 |  2013-10-09 23:15:05 
 2013-10-09 23:08:17 |  2013-10-09 23:09:00 
 2013-10-09 23:08:17 |  2013-10-09 23:08:20 
 2013-10-09 23:08:17 |  2013-10-09 23:32:04 
 2013-10-09 23:08:17 |  2013-10-10 02:00:00 
 2013-10-10 02:00:00 |  2013-10-10 02:02:03 -- splitted
 2013-10-09 23:08:17 |  2013-10-10 02:00:00 
 2013-10-10 02:00:00 |  2013-10-10 07:31:00 -- splitted
 2013-10-09 23:08:17 |  2013-10-10 02:00:00 
 2013-10-10 02:00:00 |  2013-10-10 22:41:04 -- splitted

在上面的示例中，我将时间戳分为02:00:00。

经过多次试验后，我可以将其分割如下，但不能分成不同的行。

     usage_from      |     usage_till      |     end_time_1      |     end_time_2      
---------------------+---------------------+---------------------+---------------------
 2013-10-09 23:08:17 | 2013-10-09 23:16:00 | 2013-10-09 23:16:00 | 2013-10-11 02:00:00 
 2013-10-09 23:08:17 | 2013-10-09 23:08:19 | 2013-10-09 23:08:19 | 2013-10-11 02:00:00 
 2013-10-09 23:08:17 | 2013-10-10 18:58:22 | 2013-10-10 02:00:00 | 2013-10-10 18:58:22 
 2013-10-09 23:08:17 | 2013-10-09 23:15:05 | 2013-10-09 23:15:05 | 2013-10-11 02:00:00 
 2013-10-09 23:08:17 | 2013-10-09 23:09:00 | 2013-10-09 23:09:00 | 2013-10-11 02:00:00 
 2013-10-09 23:08:17 | 2013-10-09 23:08:20 | 2013-10-09 23:08:20 | 2013-10-11 02:00:00 
 2013-10-09 23:08:17 | 2013-10-09 23:32:04 | 2013-10-09 23:32:04 | 2013-10-11 02:00:00 
 2013-10-09 23:08:17 | 2013-10-10 02:02:03 | 2013-10-10 02:00:00 | 2013-10-10 02:02:03 
 2013-10-09 23:08:17 | 2013-10-10 07:31:00 | 2013-10-10 02:00:00 | 2013-10-10 07:31:00 
 2013-10-09 23:08:17 | 2013-10-10 22:41:04 | 2013-10-10 02:00:00 | 2013-10-10 22:41:04

知道怎么做吗？最近几天我一直在苦苦挣扎我使用的是Redshift 1.0.757（基于PostgreSQL 8.02）。

Answer 1

如果 ¹ Redshift支持generate_series()的基本形式，这可能会有效。至少这在Postgres 8.3中有效：

SELECT CASE WHEN split > 0 AND g = 0 THEN usage_from
            WHEN split > 0 AND g = 1 THEN usage_till::date + '2:0'::time
            ELSE usage_from END
     , CASE WHEN split > 0 AND g = 0 THEN usage_till::date + '2:0'::time
            WHEN split > 0 AND g = 1 THEN usage_till
            ELSE usage_till END
FROM  (
   SELECT * , generate_series(0, split) AS g
   FROM  (
      SELECT *
            , (usage_till - '2:0'::time)::date
            - (usage_from - '2:0'::time)::date AS split  -- results in integer
      FROM   t
      ) sub1
   ) sub2

如何？

在内部子查询sub1中，我查找时间范围是否超过凌晨2点，并将其保存在split列中。我假设时间范围从未超过凌晨2点两次，但查询可以很容易地适应那个。 generate_series()每次自动生成1行。
在下一个子查询sub2 generate_series()中生成需要拆分的两行。
在外部SELECT中，CASE语句会相应地调整时间戳。
通常我会使用interval '2 hours'代替'2:0'::time，但我似乎记得Redshift不支持interval类型。

SQL Fiddle for Postgres 8.3.

不在Redshift？

如果Redshift仅允许generate_series()列表中的FROM而不是SELECT列表中的LATERAL JOIN，那么您就不走运了。这已经是古老的形式了。在现代Postgres中，您将使用{{1}}。你可以试试regexp_split_to_table()的运气，但这也不在Postgres 8.0中。

¹ But the manual says, generate_series() is unsupported.

除此之外，我只能想到PL / pgSQL的程序解决方案。但Redshift也可能在那里受到限制......

在postgresql中将时间戳分为两行

1 个答案:

如何？

不在Redshift？