Rails 应用程序中的 Heroku PostgreSQL GROUP_BY 错误

Question

我有一个在开发中运行良好的 Rails 应用程序 (SQLite)，但是当我通过 Heroku 部署它时抛出了很多错误，它使用了我收集的 PostgreSQL。

返回的错误信息：

        ActionView::Template::Error (PGError: ERROR:  
column "practices.id" must appear in the GROUP BY clause or be used in an aggregate function: 
SELECT "practices".* 
FROM "practices" WHERE ("practices".activity_id = 1) 
AND ("practices"."created_at" BETWEEN '2011-01-01' AND '2011-01-31') 
GROUP BY DATE(created_at) ORDER BY created_at DESC):

当我调用以下命令时会抛出这个：

def month_days_not_practiced(date = Date.today)
   p = practices.where(:created_at => date.at_beginning_of_month..date.at_end_of_month).group("DATE(created_at)").to_a.count
   days_in_month(date.year, date.month) - p
end

我真的很想保持代码干净，这样它就可以在开发和生产数据库上运行...有人能解释一下吗？

我试过这个：

def month_days_not_practiced(date = Date.today)
   p = practices.where(:created_at => date.at_beginning_of_month..date.at_end_of_month).group("practices.id, DATE(created_at)").to_a.count
   days_in_month(date.year, date.month) - p
end

无济于事...

tia.

Answer 1

Practice.joins(:foobar).group_all

def self.group_all
  group(group_all_columns)
end

def self.group_all_columns
  @group_all_columns ||= column_names.collect {|c| "#{table_name}.#{c}"}.join(",")
end

Answer 2

Practice.group(Practice.col_list)



def self.col_list
  Practice.column_names.collect {|c| "practices.#{c}"}.join(",")
end

Answer 3

您需要按所有选择列表中的列分组，所以

.group("practices.id, practices.foo, practices.bar, ..., DATE(created_at)")

您仅按 id 分组的想法是合理的（假设 id 是主键），但 PostgreSQL 仅在版本 9.1 中支持。