【判断插入数据是否重复】

public class DaoImpl {
    private Connection connection;
    // ...

    public boolean isDataExist(String data) {
        boolean exists = false;
        try {
            String sql = "SELECT COUNT(*) FROM table_name WHERE data = ?";
            PreparedStatement preparedStatement = connection.prepareStatement(sql);
            preparedStatement.setString(1, data);
            ResultSet resultSet = preparedStatement.executeQuery();
            if (resultSet.next()) {
                int count = resultSet.getInt(1);
                exists = count > 0;
            }
        } catch (SQLException e) {
            e.printStackTrace();
        }
        return exists;
    }

    public void insertData(String data) {
        boolean isExist = isDataExist(data);
        if (isExist) {
            System.out.println("Data already exists");
            return;
        }

        try {
            String sql = "INSERT INTO table_name (data) VALUES (?)";
            PreparedStatement preparedStatement = connection.prepareStatement(sql);
            preparedStatement.setString(1, data);
            preparedStatement.executeUpdate();
            System.out.println("Data inserted successfully");
        } catch (SQLException e) {
            e.printStackTrace();
        }
    }
}