如何使用SqlDataReader获取Sum结果

Question

I do a Sum() on my query but when I want to use a dataReader it is not working

I've tried this

string request = "SELECT sum(price_product) as price FROM product";
SqlCommand command = new SqlCommand(request, loaddatabaseconnexion.connexion_BDD());
SqlDataReader dataReader = command.ExecuteReader();
cout_total_stock.Text = dataReader["price"].ToString();

Answer 1

There is no need for a SqlDataReader, you can just call ExecuteScalar from the SqlCommand when your query returns a single value (Sum,Max,Min, etc)

decimal value = Convert.ToDecimal(command.ExecuteScalar());

However, if you really want to use an SqlDataReader then you should always call the Read method to 'move' the SqlDataReader internal position to the first record returned by your query

SqlDataReader dataReader = command.ExecuteReader();

// Always check if Read returns false. 
// If false there is no record to Read.
if(dataReader.Read())
   cout_total_stock.Text = dataReader["price"].ToString();