Question

I get an error in this function but I don’t know why.
Can you help me?

The error is in the row where I call executeQuery()

public static int numeroElementi(String table) throws SQLException {

    // viene reistanziata perché questa è una funziona statica!
    String DB_URL = "jdbc:mysql://localhost:3306/kmzero";
    Connection connection = DriverManager.getConnection(DB_URL, "root", "root");

    String query = "SELECT COUNT(*) AS count FROM ? ";
    PreparedStatement pStatement = connection.prepareStatement(query);
    pStatement.setString(1, table);

    try {

        ResultSet resultSet = pStatement.executeQuery();

        try {
            if (resultSet.next())
                return resultSet.getInt("count");

            else
                return 0;

        } finally {
            resultSet.close();
        }
    } finally {
        pStatement.close();
    }
}

Answer 1

I think you cannot pass the tablename (also columnNames) as a parameter and this is the time when tableName should be concatenated in your string.

String query = "SELECT COUNT(*) AS count FROM " + table;

if your table needs to be escape,

String query = "SELECT COUNT(*) AS count FROM `" + table + "`";