Sql 将时间戳打印为数字，而非人类可读

我需要一个针对psql运行的命令行，它可以：

psql database -c "select date_trunc('day', start) as date, avg(finish - start) as duration from things group by date order by date;"

但问题是这给了我人类可读的输出，也就是：

    date         |    duration
---------------------+-----------------
 2010-01-11 00:00:00 | 00:24:13.826822
 2010-01-12 00:00:00 | 00:15:42.984878
 2010-01-13 00:00:00 | 00:15:37.117834
 2010-01-14 00:00:00 | 00:13:27.868552
 2010-01-15 00:00:00 | 00:09:16.018057
 2010-01-16 00:00:00 | 00:06:39.213929

---

我想要的是unix时间戳，以秒（或毫秒）为单位，两边都是整数。我已经阅读了文档，但无法理解这一点。

我读到您可以用

SELECT date_part('epoch', now()) 

给出unix时间戳

那么你的情况呢

SELECT date_part('epoch', date_trunc('day', start) as date), 
       date_part('epoch', avg(finish - start)) as duration 
FROM things 
GROUP by date 
ORDER by date;

博士后见