在 PostgreSQL 中使用 Common Table Expression (CTE) 构建 table 时如何获得唯一字段？

Question

我正在尝试生成一系列时间戳，计算每个时间戳的星期几，并且 select 仅使用 PostGreSQL 计算周一至周六的时间戳。

这是我目前的尝试：

WITH
candidates AS (SELECT * FROM generate_series(
  date_trunc('hour', CURRENT_TIMESTAMP - INTERVAL '2 hours'),
  date_trunc('hour', CURRENT_TIMESTAMP - INTERVAL '2 hours')+INTERVAL '1 week',
  INTERVAL '1 hour')),
candidows AS (SELECT EXTRACT(DOW FROM generate_series) FROM candidates),
candidatable AS (SELECT b.date_part AS dow, a.generate_series as start_booking FROM candidates a, candidows b)
SELECT * FROM candidatable WHERE dow != 0;

返回的视图包括一个 dow 列，其行为符合我的预期，但 start_booking 列仅包含重复的相同值：

 dow |     start_booking
-----+------------------------
   2 | 2017-09-19 11:00:00+01
   2 | 2017-09-19 11:00:00+01
   2 | 2017-09-19 11:00:00+01
   2 | 2017-09-19 11:00:00+01
   2 | 2017-09-19 11:00:00+01
   2 | 2017-09-19 11:00:00+01
   2 | 2017-09-19 11:00:00+01
   2 | 2017-09-19 11:00:00+01
   2 | 2017-09-19 11:00:00+01
   2 | 2017-09-19 11:00:00+01
   2 | 2017-09-19 11:00:00+01
   2 | 2017-09-19 11:00:00+01
   2 | 2017-09-19 11:00:00+01
   3 | 2017-09-19 11:00:00+01
   3 | 2017-09-19 11:00:00+01
   3 | 2017-09-19 11:00:00+01

如果我将最后一个 SELECT 语句替换为：

SELECT * FROM candidates;

然后我试图在上面 start_booking 查看的数据是连续的，如我所料：

    generate_series
------------------------
 2017-09-19 11:00:00+01
 2017-09-19 12:00:00+01
 2017-09-19 13:00:00+01
 2017-09-19 14:00:00+01
 2017-09-19 15:00:00+01
 2017-09-19 16:00:00+01

我怎样才能让 candidates.generate_series 的数据显示为 candidatables.start_booking？

Answer 1

大胆猜测 - 你是想：

WITH
candidates AS (SELECT generate_series start_booking, EXTRACT(DOW FROM generate_series) dow FROM generate_series(
  date_trunc('hour', CURRENT_TIMESTAMP - INTERVAL '2 hours'),
  date_trunc('hour', CURRENT_TIMESTAMP - INTERVAL '2 hours')+INTERVAL '1 week',
  INTERVAL '1 hour'))
SELECT * FROM candidates WHERE dow != 0;

?..

在 PostgreSQL 中使用 Common Table Expression (CTE) 构建 table 时如何获得唯一字段？

How can I get unique fields when building a table using Common Table Expression (CTE) in PostgreSQL?

postgresql

datetime

common-table-expression

generate-series