A simple solution is.
Here Dataset ds2 contains all data, we can select required row by use for loop.
sendmail is a string variable.Same as assign to any dataset tables.
for (int i = 0; i < ds2.Tables[0].Rows.Count; i++)
{
if (ds2.Tables[0].Rows[i]["status"].ToString() == "Open")
{
sendmail += ds2.Tables[0].Rows[i]["Expr1"].ToString();
}
}