整数除法返回0 [英] Division of integers returns 0

问题描述

我觉得我缺少明显的东西。我正在尝试测试 random（）的分布。表格如下：

I feel like I'm missing something obvious. I am trying to test out the distribution of random(). Here is the table:

create table test (
  id int,
  random_float float,
  random_int int
);

这就是我想做的：

truncate table test;
insert into test (id)
values (generate_series(1,1000));
update test 
set
  random_float = random() * 10 + 1;
update test
set
  random_int = trunc(random_float);
select 
  random_int,
  count(random_int) as Count,
  cast( count(random_int) / max(id) as float) as Percent
from test
group by random_int
order by random_int;

但是，百分比列为每条记录返回零。我尝试将其强制转换为浮点数，将其转换为十进制，然后尝试将 random_int 列更改为十进制，而不是整数，始终保持相同的结果。

However, the "Percent" column returns zero for every record. I tried casting it as float, as decimal, I tried changing the random_int column to decimal instead of integer, always same result.

这是一个小提琴。

对我在做什么错有任何见解吗？

Any insight as to what I am doing wrong?

推荐答案

您应该在进行除法运算之前进行强制转换，但同时也缺少子查询以从表中获取总计数。 这里是示例。

You should cast before you divide, but also you were missing a subquery to get the total count from the table. Here's the sample.

select 
  random_int,
  count(random_int) as Count,
  cast(count(random_int) as decimal(7,2)) / cast((select count(random_int) from test) as decimal(7,2)) as Percent
from test
group by random_int
order by random_int;

这篇关于整数除法返回0的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！