往数据库加数据，判断数据库中是否已有此数据，没有才添加，有就不添加
如题，这个判断要什么写啊？

------解决方案--------------------
string sql = ("select TopicContent from T_TeacherDate");
bool hasExist = false;

DataSet ds = DbHelperSQL.Query(sql);
for (int i = 0; i < ds.Tables[0].Rows.Count; i++)
{
string ss = ds.Tables[0].Rows[i]["TopicContent"].ToString();
if (ss == model.TopicContent)
{
hasExist = true;
break;
}

}


if(!hasExist )
{
RmsystemsBLL.T_TeacherDate bll = new RmsystemsBLL.T_TeacherDate();
bll.Add(model);
}