关于一个排行的sql语句

我现在有这样 三个表
if exists (select * from dbo.sysobjects where id = object_id(N'[dbo].[HrbWeb_department]') and OBJECTPROPERTY(id, N'IsUserTable') = 1)
drop table [dbo].[HrbWeb_department]
GO

if exists (select * from dbo.sysobjects where id = object_id(N'[dbo].[Hrbweb_FK]') and OBJECTPROPERTY(id, N'IsUserTable') = 1)
drop table [dbo].[Hrbweb_FK]
GO

if exists (select * from dbo.sysobjects where id = object_id(N'[dbo].[hrbweb_bbs]') and OBJECTPROPERTY(id, N'IsUserTable') = 1)
drop table [dbo].[hrbweb_bbs]
GO

CREATE TABLE [dbo].[HrbWeb_department] (
[ModelID] [int] IDENTITY (1, 1) NOT NULL ,
[ModelTitle] [varchar] (20) COLLATE Chinese_PRC_CI_AS NULL ,
[UpModelID] [int] NULL ,
[IsLeaf] [bit] NULL ,
[PageUrl] [varchar] (255) COLLATE Chinese_PRC_CI_AS NULL ,
[ImgFileName] [varchar] (50) COLLATE Chinese_PRC_CI_AS NOT NULL ,
[sort] [int] NOT NULL
) ON [PRIMARY]
GO

CREATE TABLE [dbo].[Hrbweb_FK] (
[fankui_id] [int] IDENTITY (1, 1) NOT NULL ,
[bbs_id] [int] NULL ,
[fankui_content] [text] COLLATE Chinese_PRC_CI_AS NULL ,
[fankui_date] [datetime] NULL ,
[fankui_bm] [varchar] (50) COLLATE Chinese_PRC_CI_AS NULL
) ON [PRIMARY] TEXTIMAGE_ON [PRIMARY]
GO

CREATE TABLE [dbo].[hrbweb_bbs] (
[bbs_id] [int] IDENTITY (1, 1) NOT NULL ,
[bbs_user_name] [varchar] (50) COLLATE Chinese_PRC_CI_AS NOT NULL ,
[bbs_user_ip] [varchar] (50) COLLATE Chinese_PRC_CI_AS NOT NULL ,
[bbs_img] [int] NOT NULL ,
[bbs_title] [varchar] (200) COLLATE Chinese_PRC_CI_AS NOT NULL ,
[bbs_context] [text] COLLATE Chinese_PRC_CI_AS NULL ,
[bbs_viewCount] [int] NOT NULL ,
[bbs_shouli] [int] NOT NULL ,
[bbs_date] [datetime] NOT NULL ,
[bbs_pass] [int] NULL ,
[bbs_bm] [varchar] (50) COLLATE Chinese_PRC_CI_AS NULL
) ON [PRIMARY] TEXTIMAGE_ON [PRIMARY]
GO
部门表 HrbWeb_department 问题表 hrbweb_bbs 回复表Hrbweb_FK
我想得到的是 每个部门 的回复数除于问题数 然后 根据 这个 比率排行 谢谢大家