Question

How to make this (PostgreSQL) using Rails syntax?:

SELECT fld1, fld2
FROM
(
    SELECT fld1, fld2, count(*) as cnt FROM data WHERE fld2 not in('exclude1', 'exclude2') GROUP BY fld1, fld2 ORDER BY COUNT(*) DESC LIMIT 100
    UNION ALL
    SELECT fld1, fld2, count(*) as cnt FROM data WHERE fld2 in('exclude1', 'exclude2') GROUP BY fld1, fld2
) x
ORDER BY x.cnt DESC

I made following:

my_data = (Data.all(
    :select => sel_clause,
    :conditions => "data.fld2 not in %s" % [in_clause],
    :group => grp_clause,
    :order => 'count(*) desc',
    :limit => @max_rows) <<
    Data.all(
        :select => sel_clause,
        :conditions => "data.fld2 in %s" % [in_clause],
        :group => grp_clause).order('cnt desc')

The problem is that this << is not a classical “UNION ALL”, but joining of two arrays, and “order” can not be applied to the resulting array.

Answer 1

This is a place where I tend to use find_by_sql. The results will be returned as an array with columns requested encapsulated as attributes of the model from which you call this method.

http://ar.rubyonrails.org/classes/ActiveRecord/Base.html

~Charles~