MYSQL存储过程select语句select不正确的ID

Posted 2023-02-24

【中文标题】MYSQL存储过程select语句select不正确的ID

【英文标题】：MYSQL stored procedure select statement select incorrect ID

【发布时间】：2012-03-11 03:50:52

【问题描述】：

在存储过程方面，我不是知识最渊博的人，这个问题让我大吃一惊！

基本上我只是想运行一个简单的更新语句，但是当我在过程中运行它时，我选择更新行的用户 ID 不正确，但是如果我在过程之外运行相同的选择语句，它返回预期的结果。

DELIMITER $$
CREATE PROCEDURE catchUpBbs_Users()
  BEGIN
    DECLARE done INT DEFAULT 0;
    DECLARE deleteUser, keepUser VARCHAR(255);
    DECLARE id INT;
    DECLARE cur1 CURSOR FOR SELECT u.username, b.username, b.id from users u RIGHT     JOIN bbs_users b ON u.username = b.username WHERE u.username IS NULL;
    DECLARE CONTINUE HANDLER FOR NOT FOUND SET done = 1;     
    OPEN cur1;
        allusers: LOOP 
            FETCH cur1 INTO keepUser, deleteUser, id;
            IF done THEN 
                LEAVE allusers; 
            END IF;
IF deleteUser != 'anonymous' THEN 

-- This is where the problems start

-- Just for test purposes, returns correct id and username 
SELECT id, username FROM bbs_users WHERE username = deleteUser; 

-- Just for test purposes, return INCORRECT id, but the CORRECT username  
SELECT id, username FROM bbs_users WHERE username = 'anonymous'; 

-- The update statement that does not work as I want it to, sets the user_id to be what it already it, so no updates occur
UPDATE bbs_posts SET user_id = (SELECT id FROM bbs_users WHERE username = 'anonymous') WHERE user_id = (SELECT id FROM bbs_users WHERE username = deleteUser);

-- delete the user from the bbs_users table
DELETE FROM bbs_users WHERE username = deleteUser;

END IF;
    END LOOP allusers;
    CLOSE cur1;
END;

$$
DELIMITER ;

当我调用该过程时，两个测试选择语句返回：

1) 这些结果都是正确的

 SELECT id, username FROM bbs_users WHERE username = deleteUser;
 +------+----------+
 | id   | username |
 +------+----------+
 |   13 | deleteme |
 +------+----------+

2) ID不正确，但是用户名不正确，ID应该是1

 SELECT id, username FROM bbs_users WHERE username = 'anonymous'; 
 +------+-----------+
 | id   | username  |
 +------+-----------+
 |   13 | anonymous |
 +------+-----------+

当我运行相同的程序时，减去变量，过程外的 select 语句都返回正确的结果

1) 这些结果都是正确的

SELECT id, username FROM bbs_users WHERE username = 'deleteme';
+----+----------+
| id | username |
+----+----------+
| 13 | deleteme |
+----+----------+

2) 这些结果都是正确的

SELECT id, username FROM bbs_users WHERE username = 'anonymous';
+----+-----------+
| id | username  |
+----+-----------+
|  1 | anonymous |
+----+-----------+

我做错了什么？在使用存储过程时，在选择和变量方面有什么我错过的吗？

任何帮助或建议将不胜感激

【参考方案1】：

问题是您在游标中定义了一个名为 id 的标量变量，并且您正在选择它，因此游标内的两个 select 语句都使用该存储的标量值来引用 id .

为了获得“正确”的值，您需要消除所有歧义：

-- Just for test purposes, returns correct id and username 
SELECT b.id, b.username FROM bbs_users b WHERE b.username = deleteUser; 

-- Just for test purposes, return INCORRECT id, but the CORRECT username  
SELECT b.id, b.username FROM bbs_users b WHERE b.username = 'anonymous'; 

【讨论】：

谢谢！这解决了我的问题，你教会了我一些新东西。

【参考方案2】：

你有没有试过在 end if 和 end 循环之前重复句子“FETCH cur1 INTO keepUser, deleteUser, id”...

【参考方案3】：

以下工作是否更好。清理了您多次有效执行相同查询的位置。抱歉，如果我误解了这个问题 - 但如果我理解正确，那么下面的查询应该会更有效地运行。还会删除所有不明确的字段名称。

DELIMITER $$
CREATE PROCEDURE catchUpBbs_Users()
  BEGIN
    DECLARE done INT DEFAULT 0;
    DECLARE oldID INT;
    DECLARE newID INT;
    DECLARE cur1 CURSOR FOR 
        SELECT b.id 
        FROM users u 
        RIGHT JOIN bbs_users b 
        ON u.username = b.username 
        WHERE u.username IS NULL;

    DECLARE CONTINUE HANDLER FOR NOT FOUND SET done = 1;     

    // Get the new id
    SELECT id INTO newID FROM bbs_users WHERE username = 'anonymous';

    OPEN cur1;
        allusers: LOOP 
            FETCH cur1 INTO oldID;  // b.id

            IF done THEN 
                LEAVE allusers; 
            END IF;

            IF deleteUser != 'anonymous' THEN 

                -- Just for test purposes, returns correct id and username 
                SELECT id, username FROM bbs_users WHERE id = oldID; 

                -- Just for test purposes, return INCORRECT id, but the CORRECT username  
                SELECT id, username FROM bbs_users WHERE id = newID; 

                UPDATE bbs_posts SET user_id = newID WHERE user_id = oldID;

                -- delete the user from the bbs_users table
                DELETE FROM bbs_users WHERE id = oldID;

            END IF;
        END LOOP allusers;
    CLOSE cur1;
END;

$$
DELIMITER ;