Question

Is this code safe from SQL injections? Why?

public void AddPlayer(string username)
    {
        var query = "INSERT INTO dbo.Player(Username, RegisterDate) VALUES(@Username, @RegisterDate)";
        using (var connection = new SqlConnection(connectionString))
        using (var command = new SqlCommand(query, connection))
        {
            command.Parameters.AddWithValue("@Username", username);
            command.Parameters.AddWithValue("@RegisterDate", DateTime.Now);
            command.Connection.Open();
            command.ExecuteNonQuery();
        }
    }

    public DateTime GetRegisterDate(string username)
    {
        var query = "SELECT RegisterDate FROM dbo.Player WHERE Username = @Username";
        using (var connection = new SqlConnection(connectionString))
        using (var command = new SqlCommand(query, connection))
        {
            command.Parameters.AddWithValue("@Username", username);
            command.Connection.Open();
            return (DateTime)command.ExecuteScalar();
        }
    }

EDIT: Could injection-safe equivalent code be written using a stored procedure? If so, what the stored procedure would be like?

Answer 1

Yes, It looks safe.

Because it uses parameters.

You run a risk of SQL-injection when you create queries like
baseQueryText + " WHERE Username =" + TextBox.Text;

Reguarding the Edit: When you use a Stored Procedure you always use parameters so they are safe too. No special effort required, but you still could/should filter incoming data.