MySQL游标只获取一行

Question

我的 SQL：

CREATE PROCEDURE INV_MIN_PURCHASE_PRICE()
BEGIN
DECLARE done INT;
DECLARE current_inventory_ID INT;
DECLARE cur1 CURSOR FOR SELECT inventory_ID FROM _inventory;
DECLARE CONTINUE HANDLER FOR NOT FOUND SET done = 1;

SET done = 0;
OPEN cur1;

REPEAT

    FETCH cur1 INTO current_inventory_ID;
    UPDATE _debug SET rows=rows+1;

UNTIL done
END REPEAT;

CLOSE cur1;

END;

当我调用此过程时，MySQL 仅获取一行（_debug rows 增加 1）。为什么？？是bug吗？

Answer 1

我刚刚在 MySQL 中的存储过程遇到了同样的问题。它应该从一个表中获取某个列中具有空值的所有记录，然后从另一个表中填充该值。但是，它在一个记录后停止：

CREATE PROCEDURE `updateRecord`()
    BEGIN

    DECLARE done INT DEFAULT FALSE;
    DECLARE recordId, newValue INT;
    DECLARE current_record CURSOR FOR SELECT id FROM A where b_id is null;
    DECLARE CONTINUE HANDLER FOR NOT FOUND SET done = TRUE; 

    OPEN current_record;

    main_loop: LOOP
        FETCH current_record INTO recordId;

        IF done THEN
             LEAVE main_loop;
        END IF;

        -- fetching some value from table b
        select id into newValue from B where ...

       -- setting new value in record
       update A set b_id = newValue where id = recordId;    

      END LOOP;
    END

答案是“未找到的处理程序”不仅在游标没有返回行时执行，而且在表 B 上的选择没有返回行时执行。我的解决方案是使用由处理程序设置的第二个变量，并在选择后重置“完成”变量：

    DECLARE CONTINUE HANDLER FOR NOT FOUND SET done = TRUE, noBfound = TRUE;    

           [...]

           select id into newValue from B where ...

           IF (noBfound = TRUE) THEN 
               SET done = FALSE;
           END IF;

           [...]

补充：通过简单地在选择后重置“完成”显然可以不使用第二个变量：

    DECLARE CONTINUE HANDLER FOR NOT FOUND SET done = TRUE; 

           [...]

           select id into newValue from B where ...

           SET done = FALSE;

           [...]

Answer 2

您是否尝试过 LOOP 而不是 REPEAT 构造？似乎在 MySQL 中工作得更好。将 REPEAT to END REPEAT 部分替换为：

inv_loop: LOOP
    FETCH cur1 INTO current_inventory_ID;
    IF done = 1 THEN
        LEAVE inv_loop;
    END IF;
    UPDATE _debug SET rows=rows+1;
END LOOP;

Answer 3

IF done THEN
         LEAVE main_loop;
ELSE
         ITERATE main_loop;
END IF;