Rails + ActiveRecords：如何按日期对记录进行分组并根据条件显示其计数？

Question

I have data like this in a DB table

ID | numbers | created_at
1  |   10    | 2016-04-01
2  |   20    | 2016-04-01 
3  |   -8    | 2016-04-01
4  |    1    | 2016-04-02
5  |   81    | 2016-04-03
6  |  -12    | 2016-04-03
7  |    0    | 2016-04-03

And the desired output I'd like to get:

Date       | Greater (or even) than 0 | Smaller than 0
2016-04-01 | 2                        | 1 
2016-04-02 | 1                        | 0
2016-04-03 | 2                        | 1 

Is there a way to load this data from one query? All I can think of our subqueries and doing queries in the Rails view where I want to render the fetched data.

Answer 1

I would try something like this:

lines = Model.
  select('date, SUM(IF(number > 0, 1, 0)) as greater_count', SUM(IF(number < 0, 1, 0)) as smaller_count').
  group(:date).
  order(:date)

lines.each do |line|
  puts [line.date, line.greater_count, line.smaller_count]
end

Answer 2

Assuming your Created_at is a date with no time components... similar to spickermann's but less platform specific.

Select Created_at as Date
     , Sum(case WHEN numbers >= 0 THEN 1 Else 0 END) as GTE_0
     , Sum(case WHEN numbers < 0 THEN 1 Else 0 END) as LT_0
FROM Table
GROUP BY Created_at

What this does is evaluate the number if >=0 then it sets a value of 1 which it then sums by date for Greater than Equal to 0 (GTE_0) Similar done for LT_0 (Less than 0).