mysql - 这个 "no data"警告来自哪里？ (光标循环)

Question

CREATE TABLE INPUT ( NUM INT );
INSERT INTO INPUT VALUES (1);
CREATE TABLE OUTPUT ( NUM INT );

DELIMITER //

CREATE PROCEDURE TEST_LOOP()
BEGIN
  DECLARE NUMBER INT;

  DECLARE DONE TINYINT DEFAULT 0;
  DECLARE REC CURSOR FOR SELECT NUM FROM INPUT;
  DECLARE CONTINUE HANDLER FOR NOT FOUND SET DONE = 1;

  DELETE FROM OUTPUT;

  OPEN REC;
    L: LOOP
      FETCH REC INTO NUMBER;
      IF DONE = 1 THEN
        LEAVE L;
      END IF;

      INSERT INTO OUTPUT VALUES (NUMBER);
    END LOOP;
  CLOSE REC;
END //

DELIMITER ;

然后我运行 CALL TEST_LOOP();，该过程按预期运行(OUTPUT 表中的一条记录)，但会产生一条警告:

No data - zero rows fetched, selected, or processed.

警告从何而来？

Answer 1

实际上是an active bug in MariaDB源自 MySQL 5.5。

来自MySQL 5.5 manual ;

Before MySQL 5.6.3, if a statement that generates a warning or error causes a condition handler to be invoked, the handler may not clear the diagnostic area. This might lead to the appearance that the handler was not invoked.