Question

                        Table Folder

      Column       |           Type           |                              Modifiers                          
-------------------+--------------------------+---------------------------------
 ID                | integer                  | not null default 
 Name              | character varying        | not null
 Size              | bigint                   | not null
 Timestamp         | timestamp with time zone |

尝试计算2014年上传的所有文件。同年的每月计数。

SELECT COUNT(*) FROM  "File" WHERE "Timestamp" >  '2014-01-01 21:53:23+08'

Answer 1

SELECT TO_CHAR(Timestamp, 'Mon') AS month,
       COUNT(*) AS fileCount
FROM File
WHERE EXTRACT(YEAR FROM Timestamp) = 2014
GROUP BY TO_CHAR(Timestamp, 'Mon')

如果您想要一份显示多年的月度细分的报告，那么您可以稍微修改上述查询：

SELECT TO_CHAR(Timestamp, 'Mon') AS month,
       EXTRACT(YEAR FROM Timestamp) AS year,
       COUNT(*) AS fileCount
FROM File
WHERE EXTRACT(YEAR FROM Timestamp) IN (2014, 2015, ...)
GROUP BY TO_CHAR(Timestamp, 'Mon'),
         EXTRACT(YEAR FROM Timestamp)

Answer 2

看到您自己的查询，您似乎想要考虑从时区GMT + 8小时（新加坡，香港或其他）看到的2014年时间戳并相应计算。我认为查询应该是：

SELECT EXTRACT(MONTH FROM "Timestamp" AT TIMEZONE 'GMT-8'), COUNT(*)
FROM "File"
WHERE "Timestamp" >= timestamp with timezone '2014-01-01 00:00:00+08'
  AND "Timestamp" <  timestamp with timezone '2015-01-01 00:00:00+08'
GROUP BY EXTRACT(MONTH FROM "Timestamp" AT TIMEZONE 'GMT-8')
ORDER BY EXTRACT(MONTH FROM "Timestamp" AT TIMEZONE 'GMT-8');

由于我没有在where子句中使用“Timestamp”上的任何函数，因此索引可能更有可能用于加速查询（前提是是一个索引“时间戳“列”。

但我必须承认时区总是让我困惑。当我想谈到香港的日期时间文字和'GMT-8'（减号），当我想转换到香港时间时，为什么它是'+ 08'（加号）？不过，它应该是正确的。

按月，然后按年排序数据

2 个答案: