请帮忙解读一下这个mssql脚本每句的含义以及整个脚本的用法
if exists (select * from dbo.sysobjects where id = object_id(N'[dbo].[AutoDuty]') and OBJECTPROPERTY(id, N'IsUserTable') = 1)
drop table [dbo].[AutoDuty]
GO

CREATE TABLE [dbo].[AutoDuty] (
 [ID] [int] IDENTITY (1, 1) NOT NULL ,
 [AutoType] [char] (10) COLLATE Chinese_PRC_CI_AS NULL ,
 [AutoContent] [nvarchar] (60) COLLATE Chinese_PRC_CI_AS NOT NULL ,
 [RTime] [datetime] NOT NULL ,
 [OTime] [datetime] NULL ,
 [IsOk] [int] NOT NULL ,
 [Notes] [nvarchar] (50) COLLATE Chinese_PRC_CI_AS NULL
) ON [PRIMARY]
GO

ALTER TABLE [dbo].[AutoDuty] WITH NOCHECK ADD
 CONSTRAINT [PK_AutoNotice] PRIMARY KEY CLUSTERED
 (
  [ID]
 ) ON [PRIMARY]
GO

ALTER TABLE [dbo].[AutoDuty] ADD
 CONSTRAINT [DF_AutoDuty_AutoType] DEFAULT ('喊话') FOR [AutoType],
 CONSTRAINT [DF_AutoNotice_RTime] DEFAULT (getdate()) FOR [RTime],
 CONSTRAINT [DF_AutoNotice_IsOk] DEFAULT (0) FOR [IsOk]
GO

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

CREATE TABLE [dbo].[AutoSystem] (
 [AutoOpen] [int] NOT NULL
) ON [PRIMARY]
GO

ALTER TABLE [dbo].[AutoSystem] ADD
 CONSTRAINT [DF_AutoSystem_AutoOpen] DEFAULT (0) FOR [AutoOpen]
GO

insert into AutoSystem ([AutoOpen]) values ('1')


------解决方案--------------------
判断表是否存在
如果存在删除之
建立表
添加主键约束
添加默认值约束
下面同上
------解决方案--------------------

SQL code

--功过系统表来判断该名称的表是否存在
if exists (select * from dbo.sysobjects where id = object_id(N'[dbo].[AutoDuty]') and OBJECTPROPERTY(id, N'IsUserTable') = 1)
--存在删除该表
drop table [dbo].[AutoDuty]
GO
--创建表语法
CREATE TABLE [dbo].[AutoDuty] (
 [ID] [int] IDENTITY (1, 1) NOT NULL ,  --自增列的创建
 [AutoType] [char] (10) COLLATE Chinese_PRC_CI_AS NULL ,  --指定排序规则，详细可以查资料
 [AutoContent] [nvarchar] (60) COLLATE Chinese_PRC_CI_AS NOT NULL ,
 [RTime] [datetime] NOT NULL ,  --NOT NULL约束
 [OTime] [datetime] NULL ,
 [IsOk] [int] NOT NULL ,
 [Notes] [nvarchar] (50) COLLATE Chinese_PRC_CI_AS NULL
) ON [PRIMARY]
GO

--添加约束  （主键约束）
ALTER TABLE [dbo].[AutoDuty] WITH NOCHECK ADD
 CONSTRAINT [PK_AutoNotice] PRIMARY KEY CLUSTERED
 (
  [ID]
 ) ON [PRIMARY]
GO

--添加约束  DEFAULT 的默认值约束
ALTER TABLE [dbo].[AutoDuty] ADD
 CONSTRAINT [DF_AutoDuty_AutoType] DEFAULT ('喊话') FOR [AutoType],  
 CONSTRAINT [DF_AutoNotice_RTime] DEFAULT (getdate()) FOR [RTime],
 CONSTRAINT [DF_AutoNotice_IsOk] DEFAULT (0) FOR [IsOk]
GO