判断数据库表中字段是否为空
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string strSql = "select * from 表"SqlDataReader reader = SqlHelper.GetDataReader(strSql);if (reader.Read())                {                    DateTime? n = reader["userTime"] == DBNull.Value ? (DateTime?)null : (DateTime)reader["userTime"];                    int? m = Convert.IsDBNull(reader["userName"]) ? (int?)null : int.Parse(reader["userName"].ToString());                }                else                {                    reader.Close();                }