java - PrepareStatement 错误

Question

我在这个函数中遇到错误，但我不知道为什么。你能帮帮我吗？

错误在我调用 executeQuery()

的行中

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

我认为您不能将 tablename(还有 columnNames)作为参数传递，此时 tableName 应该在您的字符串。

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

如果你的表需要转义，

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