sql - PostgreSQL如何获取某些行的总和的平均值

Question

如果标题不是很贴切，我深表歉意，但我在制定一个简洁的标题时遇到了一些麻烦。不管怎样，我有一个记录一个人所处状态的表格。它看起来像:

id, login, state, duration, started_at
1, pdiddy, working, 1200, 2018-05-25 08:30:00
2, pdiddy, lunch, 120, 2018-05-25 9:00:00
3, pdiddy, on_call, 65, 2018-05-25 12:30:00
4, pdiddy, available, 1115, 2018-05-25 12:30:00
5, pdiddy, working, 143, 2018-05-25 12:30:00
6, pdiddy, break1, 150, 2018-05-25 12:30:00
7, pdiddy, working, 2400, 2018-05-25 12:30:00
8, pdiddy, break2, 110, 2018-05-25 12:30:00

I need to get an average for only labor-related durations on a day-by-day basis for each user. So basically I need to add up the durations for everything other than "lunch", "break1", and "break2" for any given day and get the average for it.

I tried to do this like this, but the problem with this is that it doesn't add up the labor-related logs before averaging. I can't figure out how to do that.

SELECT
    log.login,
    AVG(log.duration) FILTER (WHERE log.state NOT IN ('lunch', 'break1', 'break2')) AS "labor_average"
FROM
    log
GROUP BY 1

显然，我不希望有人为我做这件事。我只需要指出正确的方向。我显然离解决方案还有很长的路要走，所以我只需要朝着正确的方向前进。非常感谢您!

Answer 1

我想你想要总和除以天数:

SELECT l.login,
       (SUM(l.duration) FILTER (WHERE l.state NOT IN ('lunch', 'break1', 'break2')) /
        COUNT(DISTINCT date_trunc('day', l.started_at)
       ) AS labor_average
FROM log l
GROUP BY l.login