Rails / SQL：如何订购分组记录

Question

I have a tabel called SessionHistory with the column of ip .

I now want to first group the records having the same ip and then sort the groups by the number of records in each group.

For Example:

Record1: ip = 3
Record2: ip = 1
Record3: ip = 2
Record4: ip = 1
Record5: ip = 2
Record6: ip = 1

grouped ...

Group1:
    Record1: ip = 3
Group2:
    Record2: ip = 1
    Record4: ip = 1
    Record6: ip = 1
Group3:
    Record3: ip = 2
    Record5: ip = 2

sorted ...

Group1:
    Record2: ip = 1
    Record4: ip = 1
    Record6: ip = 1
Group2:
    Record3: ip = 2
    Record5: ip = 2
Group3:
    Record1: ip = 3

My Approach:

        - @devices = SessionHistory.all.group_by(&:ip)
        - @devices.keys.sort.each do |ip| # not sorted after size of group!
            %h1= ip
            %h4= @devices[ip].first.name # somehow not giving anything!
            - @devices[ip].each do |session|
                %h1.tiny= session.name

There are some problems though, the groups are obviously not sorted after their size and I am not able to read values from single records in one group.

Answer 1

Grouped SQL queries are returned as a Hash, where the keys are the values of IPs which records are grouped by and the values are the objects themselves. To sort that kind of results you could use the .sort method to order by hash values count:

@devices = SessionHistory.all.group_by(&:ip)
@devices.sort!{|a,b| b.values.count <=> a.values.count }

Or reverse ordering as simple as calling .reverse

@devices = SessionHistory.all.group_by(&:ip)
@devices.sort!{|a,b| b.values.count <=> a.values.count }.reverse!

Not an SQL solution, but at least it is clean and just works™