Multi-resultsets are sent up by stored procedures if more than one resultset was generated inside of it:

CREATE TEMPORARY TABLE ins ( id INT );
DROP PROCEDURE IF EXISTS multi;
DELIMITER $$
CREATE PROCEDURE multi() BEGIN
  SELECT 1;
  SELECT 1;
  INSERT INTO ins VALUES (1);
  INSERT INTO ins VALUES (2);
END$$
DELIMITER ;

CALL multi();
DROP TABLE ins;

results in:

SERVER_MORE_RESULTS_EXISTS is set to indicate that more resultsets will follow.

The trailing OK_Packet is the response to the CALL statement and contains the affected rows of the last statement. In our case we INSERTed 2 rows, but only the affected_rows of the last INSERT statement is returned as part of the OK_Packet. If the last statement is a SELECT the affected rows is 0.

The client has to announce that it wants multi-resultsets by either setting the CLIENT_MULTI_RESULTS or CLIENT_PS_MULTI_RESULTS capability.

A multi-statement is allowing COM_QUERY to send more than one query to the server, separated by a ';'.

The client has to announce that it wants multi-statements by either setting the CLIENT_MULTI_STATEMENTS capability or by using COM_SET_OPTION.

Allows to enable and disable:

for the current connection. The option operation is one of:

On success it returns a EOF_Packet otherwise a ERR_Packet.

Fetch a row from a existing resultset after a COM_STMT_EXECUTE.

Todo.  lookup example