mysql - Rails 3 在 where 子句中使用 sum()

Question

我的 where 子句有点问题。

PurchasePosition.where(:purchase_order_id => 996).where('sum(pallet_purchase_position_assignments.quantity) < purchase_positions.quantity').includes(:pallet_purchase_position_assignments)

我的模型:

class PurchasePosition < ActiveRecord::Base
  has_many :pallet_purchase_position_assignments, :class_name => "PalletPurchasePositionAssignment"
  has_many :pallets, :class_name => "Pallet", :through => :pallet_purchase_position_assignments
end

class Pallet < ActiveRecord::Base
  has_many :pallet_purchase_position_assignments, :class_name => "PalletPurchasePositionAssignment"
  has_many :purchase_positions, :class_name => "PurchasePosition", :through => :pallet_purchase_position_assignments
end

class PalletPurchasePositionAssignment < ActiveRecord::Base
  belongs_to :pallet, :class_name => "Pallet", :foreign_key => "pallet_id"
  belongs_to :purchase_position, :class_name => "PurchasePosition", :foreign_key => "purchase_position_id"
end

我得到的只是一个 Mysql 错误

ActiveRecord::StatementInvalid: Mysql2::Error: Invalid use of group function

我完全不知道我的错误在哪里:-/

有人能解决我的问题吗？

迈克尔

Answer 1

您收到的错误是因为您没有使用 group by 子句。

在 mysql 和大多数数据库中，如果你想在选择中使用求和(或任何按列分组)而不是使用 HAVING 子句而不是 WHERE 子句

PurchasePosition.where(:purchase_order_id => 996).having('sum(pallet_purchase_position_assignments.quantity) < purchase_positions.quantity').includes(:pallet_purchase_position_assignments).sum("pallet_purchase_position_assignments.quantity

例如，如果我有一个像这样的表:

 create_table "leaders", :force => true do |t|
   t.integer  "leaderable_id"
   t.string   "leaderable_type"
   t.integer  "county_id"
   t.integer  "us_state_id"
   t.integer  "recruits"
   t.integer  "hours"
   t.datetime "created_at"
   t.datetime "updated_at"
   t.datetime "last_run_dt"
 end

然后我可以像这样创建一个 having 查询

Leader.having("sum(hours) > 150").group(:leaderable_type).sum(:hours)

我不确定我的语法是否适合您的查询，但您应该能够使用 having 子句和组子句修复它。