da.SelectCommand.CommandText="select au_id,au_fname,au_lname from authors";

    da.Fill(ds,"Author");

    da.SelectCommand.CommandText="select au_id,title_id from titleauthor";

    da.Fill(ds,"TitleAuthor");

    da.SelectCommand.CommandText="select title_id,title from titles";

    da.Fill(ds,"Titles");

    //

    ds.Tables["Titles"].Columns["title_id"].Unique=true;

    ds.Tables["Titles"].Columns["title_id"].AllowDBNull=false;

    ds.Tables["Titles"].PrimaryKey=new DataColumn[]{ds.Tables["Titles"].Columns["title_id"]};

    //

    ds.Tables["Author"].Columns["au_id"].Unique=true;

    ds.Tables["Author"].Columns["au_id"].AllowDBNull=false;

    ds.Tables["Author"].PrimaryKey=new DataColumn[]{ds.Tables["Author"].Columns["au_id"]};

    //

    ds.Tables["TitleAuthor"].PrimaryKey=new DataColumn[]{ds.Tables["TitleAuthor"].Columns["au_id"],

     ds.Tables["TitleAuthor"].Columns["title_id"]};

    //定义约束

    ForeignKeyConstraint fk1=new ForeignKeyConstraint("authorstitleauthor",ds.Tables["Author"].Columns["au_id"],

     ds.Tables["TitleAuthor"].Columns["au_id"]);

    ds.Tables["TitleAuthor"].Constraints.Add(fk1);

    ForeignKeyConstraint fk2=new ForeignKeyConstraint(

     "titlestitleauthor",ds.Tables["Titles"].Columns["title_id"],

     ds.Tables["TitleAuthor"].Columns["title_id"]);

    ds.Tables["TitleAuthor"].Constraints.Add(fk2);

    this.dataGrid1.DataSource=ds;

    this.dataGrid1.DataMember="TitleAuthor";