C#

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public static bool ExecuteSQLQuery(NpgsqlCommand cmdText, out DataTable dataTable)
        {
            try
            {
                string connectionString = ConfigurationManager.AppSettings["connectionString"];

                NpgsqlConnection sqlConnection = new NpgsqlConnection(connectionString);
                sqlConnection.Open();

                cmdText.Connection = sqlConnection;

                dataTable = new DataTable();
                dataTable.Load(cmdText.ExecuteReader(CommandBehavior.CloseConnection));

                sqlConnection.Close();

                return true;
            }
            catch(Exception ex)
            { dataTable = new DataTable();  return false; }
        }

DataTable dataTable = new DataTable();
            NpgsqlCommand sqlCommand = new NpgsqlCommand("SELECT * FROM users.users WHERE (email ilike @email or username ilike @username)");
            sqlCommand.Parameters.AddWithValue("email", NpgsqlTypes.NpgsqlDbType.Varchar, email);
            sqlCommand.Parameters.AddWithValue("username", NpgsqlTypes.NpgsqlDbType.Varchar, username);

DatabaseConnectivity.ExecuteSQLQuery(sqlCommand, out dataTable)

public static bool ExecuteSQLNonQuery(NpgsqlCommand cmdText)
        {
            try
            {
                string connectionString = ConfigurationManager.AppSettings["connectionString"];

                NpgsqlConnection sqlConnection = new NpgsqlConnection(connectionString);
                sqlConnection.Open();

                cmdText.Connection = sqlConnection;
                cmdText.ExecuteNonQuery();

                sqlConnection.Close();

                return true;
            }
            catch (Exception ex)
            { return false; }
        }