Mysql 未找到的处理程序是如何工作的，它的用途是什么？

对MySQL来说还是有点陌生。我想知道什么是未找到的处理程序，它是如何工作的，最重要的是：它的用途是什么？

处理程序用于捕获异常

从游标读取时，如果读取超过游标的末尾，则会引发未找到异常，而不是返回无休止的NULL流，因此必须捕获此异常

DECLARE val1 INT DEFAULT NULL;
DECLARE done TINYINT DEFAULT FALSE;

DECLARE c1 CURSOR FOR SELECT id FROM t1;

-- when the NOT FOUND condition fires, "done" -- which defaults to FALSE -- will be set to true,
-- and since this is a CONTINUE handler, execution continues with the next statement.   

DECLARE CONTINUE HANDLER FOR NOT FOUND SET done = TRUE;

OPEN c1;

my_loop: 
LOOP

  FETCH NEXT FROM c1 INTO val1; 
  IF done THEN -- this will be true when we are out of rows to read, so we go to the statement after END LOOP.
    LEAVE my_loop; 
  ELSE
    -- maybe do more stuff here
  END IF;
END LOOP;

-- procedure continues here...

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部分复制自我的示例。

你可以试试谷歌。看看