How can i read the return value from "Select Where" statement , every time i run no return value appear in the label, and no syntax error.
command.CommandText = "select product_price from product where product_name='"+x+"';";
connection.Open();
Reader = command.ExecuteReader();
while(Reader.Read()){
Price_label.Content = "" + Reader.GetString(0);
}
connection.Close();
If the product_price column is not of type TEXT in MySQL, the Reader.GetString(0) will (depending on how the reader was implemented by Oracle) throw an Exception or return an empty string. I would think the latter is happening.
Retrieving the value through a DataReader requires you to know the data type. You can not simply read a string for every type of field. For example, if the field in the database is an Integer, you need to use GetInt32(...). If it is a DateTime use GetDateTime(...). Using GetString on a DateTime field won't work.
EDIT
This is how I'd write this query:
using (MySqlConnection connection = new MySqlConnection(...))
{
connection.Open();
using (MySqlCommand cmd = new MySqlCommand("select product_price from product where product_name='@pname';", connection))
{
cmd.Parameters.AddWithValue("@pname", x);
using (MySqlDataReader reader = cmd.ExecuteReader())
{
StringBuilder sb = new StringBuilder();
while (reader.Read())
sb.Append(reader.GetInt32(0).ToString());
Price_label.Content = sb.ToString();
}
}
}
x?connection, not conn as conn doesn't exist :-)To append to my comment, your approach has three problems which are not part of your problem:
"" + string for casting is...uhhh...not good and not necessary.So, a more correct version for your code would look like this:
// using utilizes the IDisposable-Interface, whcih exists to limit the lifetime
// of certain objects, especially those which use native resources which
// otherwise might be floating around.
using(YourConnectionType connection = new YourConnectionType("connectionstring"))
{
connection.Open(); // You might want to have this in a try{}catch()-block.
using(YourCommandType command = connection.CreateCommand())
{
command.CommandText = "select product_price from product where product_name=@NAME;";
command.Parameters.Add("NAME", YourTypes.VarChar);
command.Parameters[0].Value = x; // For your own sanity sake, rename that variable!
using(YourReaderType reader = command.ExecuteReader())
{
while(reader.Read()) // If you're expecting only one line, change this to if(reader.Read()).
{
Price_label.Content = reader.GetString(0);
}
}
}
} // No need to close the conenction explicit, at this point connection.Dispose()
// will be called, which is the same as connection.Close().
you have to create a variable of your reader
command.CommandText = "select product_price from product where product_name='"+x+"';";
try {
connection.Open();
SqlReader reader = command.ExecuteReader();
while(reader.Read()){
Price_label.Content = "" + Reader.GetString(0);
}
} catch (Exception) {}
finally {
connection.Close();
}
reader, but Reader to actually read the value.
You should write @pname without '' otherwise it won't work.
instead of:
select product_price from product where product_name='@pname'
you should write like this:
select product_price from product where product_name=@pname
"" +habit for typecasting. Secondly, you want to look at parameterized queries. Additionally, you should utilize theIDispoableinterface viausing().