## Cursors and streaming

| At the time of writing, you cannot use the following features if you connect to your database through ProxySQL. If you try, you will see this error message:
    RECEIVED AN UNKNOWN COMMAND: 28 -- PLEASE REPORT A BUG
This is because the proxy does not handle a type of command (`COM_STMT_FETCH`) that is required to fetch rows from a cursor.

By default, prepared query execution fetches all rows, you can use a `Cursor` to control the amount of rows you want to read:

    connection
      .prepare("SELECT * FROM users WHERE age > ?")
      .onComplete(ar1 -> {
      if (ar1.succeeded()) {
        PreparedStatement pq = ar1.result();

        // Create a cursor
        Cursor cursor = pq.cursor(Tuple.of(18));

        // Read 50 rows
        cursor
          .read(50)
          .onComplete(ar2 -> {
          if (ar2.succeeded()) {
            RowSet<Row> rows = ar2.result();

            // Check for more ?
            if (cursor.hasMore()) {
              // Repeat the process...
            } else {
              // No more rows - close the cursor
              cursor.close();
            }
          }
        });
      }
    });

Cursors shall be closed when they are released prematurely:

    cursor
      .read(50)
      .onComplete(ar2 -> {
      if (ar2.succeeded()) {
        // Close the cursor
        cursor.close();
      }
    });

A stream API is also available for cursors, which can be more convenient, specially with the Rxified version.

    connection
      .prepare("SELECT * FROM users WHERE age > ?")
      .onComplete(ar1 -> {
      if (ar1.succeeded()) {
        PreparedStatement pq = ar1.result();

        // Fetch 50 rows at a time
        RowStream<Row> stream = pq.createStream(50, Tuple.of(18));

        // Use the stream
        stream.exceptionHandler(err -> {
          System.out.println("Error: " + err.getMessage());
        });
        stream.endHandler(v -> {
          System.out.println("End of stream");
        });
        stream.handler(row -> {
          System.out.println("User: " + row.getString("last_name"));
        });
      }
    });

The stream read the rows by batch of `50` and stream them, when the rows have been passed to the handler, a new batch of `50` is read and so on.

The stream can be resumed or paused, the loaded rows will remain in memory until they are delivered and the cursor will stop iterating.