三层架构，使用DLL

//method can be used for executing insert,delete,update sql commands

  public bool exenonquerycmds(string query)

{

    bool exestatus;

    sqlcommand cmd=new sqlcommand(query,con);

    int re=cmd.executenonquery();

   if(re>0)

   {

     exestatus=true;

   }

   else

    {

    exestatus=false;

   }

   return exestatus;

  

}

 

//method can be used for retrieving data from table

public datatable gettabledata(string query)

{

    Datatable dt=new Datatable();

    sqldatadapter da=new SqlDataAdapter(query,con);

    da.Fill(dt);

    return dt;

}