获取ActiveRecord中每个组的最小/最大值

Question

这是一个古老的问题,给定一个具有属性"类型","变化"和"价格"的表格,您可以获取每种类型的最低价格的记录.

在SQL中,我们可以做这样的:

select f.type, f.variety, f.price   
from (  select type, min(price) as minprice from table group by type ) as x  
inner join table as f on f.type = x.type and f.price = x.minprice;`

我们也许可以通过以下方式模仿:

minprices = Table.minimum(:price, :group => type)  
result = []
minprices.each_pair do |t, p|  
   result << Table.find(:first, :conditions => ["type = ? and price = ?", t, p])
end

有没有比这更好的实施？

Answer 1

Table.minimum(:price, :group => :type)

见http://api.rubyonrails.org/classes/ActiveRecord/Calculations.html#method-i-minimum更多信息,.