将整数转换为数字，然后记录日志

Question

我有一张带有2个时间戳的红移表，存储为整数。我想约会两个时间戳的差异，从秒转换为几天，然后记录结果的日志。

e.g：

select cast(t1 - t2 as numeric)/86400 as diff from mytable limit 5

哪个收益率：

      diff
1 0.000011
2 1.379166
3 1.365104
4 1.357002
5 17.356759

但是，当我添加日志功能时，语句失败：

select log(cast(t1 - t2 as numeric)/86400) as diff from mytable limit 5

的产率：

Function "log(numeric,numeric)" not supported.

这是令人惊讶的，因为日志函数在同一个表中的数字和整数列上运行得很好。在拍摄日志之前，我需要在演员表演后做一些魔术吗？或者我应该投射不同的数据类型？

奇怪的是，这句话很有用：

select log(cast(1410551376-1310551376 as numeric)/86400) as diff

得到以下特性：

      diff
1 3.063486

/ edit：如果删除显式强制转换，我也会得到同样的错误：

select log((t1 - t2)/86400.0) as diff from mytable limit 5

Answer 1

Postgres长期支持numeric作为log()的论据（RedShift基于Postgres）。也许曾几何时，它只允许加倍，所以这应该有效：

select log(cast(t1 - t2 as double precision)/86400.0) as diff
from mytable
limit 5;

Answer 2

你默认为整数运算，改为强制浮点

select log(cast(t1 - t2 as numeric)/86400.0) as diff from mytable limit 5

另外，请确保t1大于t2