Question

如何使用Rails语法制作这个（PostgreSQL）？：

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

我做了以下：

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')

问题是这个＆lt;＆lt;不是经典的“UNION ALL”，而是连接两个数组，并且“order”不能应用于生成的数组。

Answer 1

这是我倾向于使用find_by_sql的地方。结果将作为一个数组返回，其中请求的列被封装为模型的属性，您可以从中调用此方法。

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

〜查尔斯〜

Rails - “all all”之后的“order by”

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