private void button2_Click(object sender, EventArgs e)
        {
            if (dataGrid1[dataGrid1.CurrentCell] != null)
            {
                string sql = "select specialtyname from specialtyinfo where specialtyid=" + ds.Tables["specialty"].Rows[dataGrid1.CurrentCell.RowNumber][0].ToString().Trim() + "and specialtyid not in (select distinct specialtyinfo.specialtyid from classinfo inner join specialtyinfo on classinfo.specialtyname=specialtyinfo.specialtyname)";
                OleDbCommand cmd = new OleDbCommand(sql, connection1);
                OleDbDataReader dr;
                dr = cmd.ExecuteReader();
                if (!dr.Read())
                {
                    MessageBox.Show("删除专业'" + ds.Tables["specialty"].Rows[dataGrid1.CurrentCell.RowNumber][1].ToString().Trim() + "'失败,请先删除与此专业相关的班级", "提示");
                    dr.Close();
                }
                else
                {
                    dr.Close();
                    sql = "delete * from specialtyinfo where specialtyname not in (select distinct specialtyname from classinfo) and specialtyid=" + ds.Tables["specialty"].Rows[dataGrid1.CurrentCell.RowNumber][0].ToString().Trim();
                     = sql;
                    cmd.ExecuteNonQuery();
                    MessageBox.Show("删除专业'" + ds.Tables["specialty"].Rows[dataGrid1.CurrentCell.RowNumber][1].ToString().Trim() + "'成功", "提示");
                }
            }
        }

我自己测试好了。谢谢。。