Performs a positional update on the current query. Is better to avoid the positional updates and deletes. Is recommended to use the CommandText or PreparedQuery and ExecuteNonQuery to execute an "update" query. Positional operations are sometimes dangerous to the data integrity.
Return value:
This function returns null.
Example
...
DataSet.CommadText="select * from my_table";
DataSet.ExecuteQuery();
...
//-----------------------------------------------------------------//
DataSet.FieldValues["my_field"]="my new value";
DataSet.Update();
//-----------------------------------------------------------------//
// is equivalent with
var current_id= DataSet.FieldValues["id"].ToNumber();
DataSet.CommandText="update my_table set my_field=\"my new value\" where id=$current_id";
//-----------------------------------------------------------------//