Question

在Why Use TimescaleDB over Relational DBs?文章中，给出了针对双时态用例的以下示例

SELECT
    time_bucket('1 day', time) AS day,
    asset_code,
    last(price, time_recorded)
FROM prices
WHERE time > '2017-01-01'
GROUP BY day, asset_code
ORDER BY day DESC, asset_code;

如果我们假设prices表包含recorded_by列，是否可以编写一个同时返回time_recorded和recorded_by列的查询？

例如，给出以下输入：

+------------------+------------+-------+------------------+-------------+
|       time       | asset_code | price |  time_recorded   | recorded_by |
+------------------+------------+-------+------------------+-------------+
| 2019-08-08 12:00 |          1 | 9     | 2019-08-08 12:00 | foo         |
| 2019-08-09 15:30 |          1 | 10    | 2019-08-09 15:30 | foo         |
| 2019-08-08 12:00 |          1 | 9.5   | 2019-08-09 15:00 | bar         |
+------------------+------------+-------+------------------+-------------+

您期望获得以下输出：

+------------+------------+-------+------------------+-------------+
|    day     | asset_code | price |  time_recorded   | recorded_by |
+------------+------------+-------+------------------+-------------+
| 2019-08-09 |          1 | 10    | 2019-08-09 15:30 | foo         |
| 2019-08-08 |          1 | 9.5   | 2019-08-09 13:00 | bar         |
+------------+------------+-------+------------------+-------------+

Answer 1

事实证明，您实际上可以使最后一个函数的两个参数都引用同一列，例如

SELECT
    time_bucket('1 day', time) AS day,
    asset_code,
    last(price, time_recorded) AS price,
    last(time_recorded, time_recorded) AS time_recorded,
    last(recorded_by, time_recorded) AS recorded_by
FROM prices
WHERE time > '2017-01-01'
GROUP BY day, asset_code
ORDER BY day DESC, asset_code;

是否可以从Timescale的双时态表访问审核数据

1 个答案: