Question

我正在做一些与不同表格的时间序列数据匹配的工作。作为示例，该表具有1秒时间序列的列和最近的小时＆＃39;列如：

"datetime"                  "closesthourdatetime"
"01/01/2005 00:30:00"       "01/01/2005 01:00:00"
"01/01/2005 00:30:01"       "01/01/2005 01:00:00"
"01/01/2005 00:30:02"       "01/01/2005 01:00:00"

如果我跑

    SELECT time_series_only.closesthourdatetime
    FROM measdata.time_series_only
    WHERE time_series_only.datetime = time_series_only.closesthourdatetime

与运行

不同，我没有得到我所希望的所有结果

  SELECT DISTINCT time_series_only.closesthourdatetime
  FROM measdata.time_series_only

我在哪里。

我猜测这是因为pgsql日期时间实际上是数字值，时间是一天的一部分，所以毫秒可能不完全匹配，我并不关心。

有没有办法查询，但指定最近的秒或分钟 WHERE time_series_only.datetime = time_series_only.closesthourdatetime 没有像这样的复杂且可能很慢的查询？：

  SELECT DISTINCT time_series_only.closesthourdatetime
  FROM measdata.time_series_only
  --WHERE 
  --time_series_only.datetime = time_series_only.closesthourdatetime
  /*EXTRACT (YEAR FROM time_series_only.datetime)   = EXTRACT(YEAR FROM time_series_only.closesthourdatetime)
  AND EXTRACT (MONTH FROM time_series_only.datetime)    = EXTRACT(MONTH FROM time_series_only.closesthourdatetime)
  AND EXTRACT (DAY FROM time_series_only.datetime)  = EXTRACT(DAY FROM time_series_only.closesthourdatetime)
  AND EXTRACT (HOUR FROM time_series_only.datetime)     = EXTRACT(HOUR FROM time_series_only.closesthourdatetime)
  AND EXTRACT (MINUTE FROM time_series_only.datetime) = EXTRACT(MINUTE FROM time_series_only.closesthourdatetime)
  AND EXTRACT (SECOND FROM time_series_only.datetime) = EXTRACT(SECOND FROM time_series_only.closesthourdatetime)

Answer 1

您可以使用以下where子句获得预期结果：

WHERE datetime >= closesthourdatetime - INTERVAL '30 MINUTE'
AND   datetime <  closesthourdatetime + INTERVAL '30 MINUTE'

此处，latesthourdatetime 01/01/2005 01:00:00将匹配[01/01/2005 00:30:00, 01/01/2005 01:30:00)范围内所有日期时间，其中第二个日期是独占的。

SQL Fiddle for test/edge cases

postgresql WHERE timea = timeb，如何指定精度？

1 个答案: