mysql - Cursor incorrect integer value 错误

Question

我正在尝试在 MySQL 中制作我的第一个游标，但我收到一个错误。它说不正确的整数值。我在想这会从列 customer_Id 中获取第一行中的值，并将其存储到 IdValue 变量中。如何正确编码并修复此错误？

DELIMITER $$

CREATE PROCEDURE CursorProcedure()
BEGIN
DECLARE IdValue int;
DECLARE  myCursor CURSOR FOR 
SELECT customer_Id FROM customers;

OPEN myCursor;
FETCH myCursor INTO IdValue;
CLOSE myCursor;
SELECT IdValue;
END$$
DELIMITER ;

Answer 1

DROP PROCEDURE IF EXISTS CursorProcedure;
DELIMITER $$
CREATE PROCEDURE CursorProcedure()
BEGIN
    DECLARE done INT DEFAULT FALSE;
    DECLARE IdValue int;
    DECLARE myCursor CURSOR FOR SELECT customer_Id FROM customers;
    DECLARE CONTINUE HANDLER FOR NOT FOUND SET done = TRUE;

    OPEN myCursor;
    read_loop: LOOP
        FETCH myCursor INTO IdValue;
        IF done THEN
            LEAVE read_loop;
        END IF;
        -- 
        --  YOU ARE IN YOUR READ LOOP
        --  DO SOMETHING WITH IT HERE
        --
    END LOOP;
    CLOSE myCursor;
END$$
DELIMITER ;

但是在“do something with it here”中，不要对它做SELECT，因为它会生成多个结果集。做一些有意义的事情。

关于 Cursors 的手册页.

顺便说一句，游标很少是你的 friend 。他们非常慢。仅在紧急情况下使用它们。