Question

An SQL aggregate function counting number of name enteries in DB.

string cnnStr = ConfigurationManager.ConnectionStrings["LGFConnectionString"].ConnectionString;
string mySQL = "SELECT COUNT(*) FROM  " + which.table + " WHERE " + which.column + " = ?pram;";
string value = null;

using (MySqlConnection cnn = new MySqlConnection(cnnStr))
{
        using (MySqlCommand cmd = new MySqlCommand(mySQL, cnn))
        {
            MySqlParameter param = new MySqlParameter("?pram", MySqlDbType.VarChar, 128);
            param.Value = which.text;
            cmd.Parameters.Add(param);

            cnn.Open();

            value = cmd.ExecuteScalar() as string;
            value = cmd.ExecuteScalar().ToString();

            cnn.Close();
        }
}

Notice that I have called cmd.ExecuteScalar twice. Interesting part is that the query returns different results.

value = cmd.ExecuteScalar() as string;

doesn’t return the correct value. It returns null for both if name is present or missing in the name column.

value = cmd.ExecuteScalar().ToString();

returns correctly. This returns “1” if present and “0” if missing.

In searching the web, I haven’t found an understandable explanation.

I have read that if name is missing from name column, then cmd.ExecuteScalar will return null.

What is the difference between:

value = cmd.ExecuteScalar() as string;
value = cmd.ExecuteScalar().ToString();

Thank you,
deDogs

Answer 1

as in docs

The as operator is used to perform conversions between compatible types.

The as operator is like a cast except that it yields null on conversion failure instead of raising an exception

// if cmd.ExecuteScalar() is string then return string
// if not then return null
// this will return null, because cmd.ExecuteScalar() won't return string
// for your code it should return Int32
value = cmd.ExecuteScalar() as string;

ToString() in docs

ToString is the major formatting method in the .NET Framework. It
converts an object to its string representation so that it is suitable
for display. (For information about formatting support in the .NET
Framework, see Formatting Types.)

// return a string that represents the current object
// will return correct value because it casts Int32 value to string value
value = cmd.ExecuteScalar().ToString();