2、恢复Northwind数据库,C盘根目录下的'Northwind.bak'备份文件：
       a、将数据库置于离线状态
           ALTER DATABASE 'Northwind' SET OFFLINE WITH ROOLBACK IMMEDIATE;
       b、恢复Northwind数据库
           RESTORE DATABASE 'Northwind' FROM DISK = 'C:\Northwind.bak';
       c、将数据库置于在线状态
           ALTER DATABASE 'Northwind' SET ONLINE WITH ROOLBACK IMMEDIATE;

  恢复数据库：
  关键字：Alter Database 被恢复的数据库名 Set Offline with Rollback immediate;
            restore database 被恢复的数据库名 from disk = '备份文件路径';
            Alter Database 被恢复的数据库名 Set OnLine With rollback Immediate;

/////////////////////
    string sql = "Alter Database db Set Offline with Rollback immediate;"; //db 是要备份的数据库名
    sql +=  "restore database db from disk = '" ;
    sql += Server.MapPath("").ToString() +"\\";
    sql += bakname + "'";  //bakname 是备份文件名
    sql += "Alter Database db Set OnLine With rollback Immediate;";
    try
    {
     连接 master 数据库 ;
     执行 sql  语句;
     Response.Write("<script language=javascript>alert('数据恢复成功！');</script>");
    }
    catch(Exception ex)
    {
     Response.Write("<script language=javascript>alert('数据恢复失败！');</script>");
     this.Label2.Text = ex.ToString();
    }

备份数据库：

关键字：backup database 被备份的数据库名 to disk ='备份文件路径';
//////////////////////     
 string sql = "backup database db to disk = '" + Server.MapPath("").ToString() +"\\"
    + bakname