MySql 获取游标到变量返回空

Question

问题在于 FETCH INTO(在循环中)没有将值放入变量中。我看过 MYSQL | SP | CURSOR - Fetch cursor into variable return null但该表已填充。

事务表如下所示:

CREATE TABLE `transactionentry` (
    `transactionid` bigint(20) NOT NULL AUTO_INCREMENT,
    ...
    PRIMARY KEY (`transactionid`),
    ...
) ENGINE=InnoDB AUTO_INCREMENT=651 DEFAULT CHARSET=utf8;

存储过程:

PROCEDURE `doTxnHouseKeeping`()
BEGIN
    -- Loop invariant
    DECLARE noEntries INTEGER DEFAULT FALSE;
    -- Error codes
    DECLARE code CHAR(5) DEFAULT '00000';
    DECLARE msg TEXT;
    -- Txn vars
    DECLARE transactionId BIGINT(20);
    DECLARE lastTransactionId BIGINT(20) DEFAULT 0;
    -- testing
    DECLARE counter INT(11) DEFAULT 0;

    DEClARE txnEntryCur CURSOR FOR 
        SELECT 
            `transactionid`
        FROM 
            `transactionentry`
        LIMIT 1;

    DECLARE CONTINUE HANDLER FOR 
        NOT FOUND SET noEntries = TRUE;  

    DECLARE EXIT HANDLER FOR
        SQLEXCEPTION
            BEGIN
                GET DIAGNOSTICS CONDITION 1
                code = RETURNED_SQLSTATE, msg = MESSAGE_TEXT;
                SELECT CONCAT('Error fetching transaction entries code: ', code, ' message: ', msg);
            END;

    OPEN txnEntryCur;

    mainLoop: LOOP
        FETCH 
            txnEntryCur 
        INTO 
            transactionId;

        IF noEntries THEN 
            LEAVE  mainLoop;
        END  IF;

        IF transactionId IS NOT NULL THEN
            INSERT INTO debugTable (`bigintval`) VALUES (transactionId);
        ELSE
            INSERT INTO debugTable (`strval`) VALUES ('transactionId is NULL');
        END IF;

        SET counter = counter + 1;
    END LOOP mainLoop;

    CLOSE txnEntryCur;

    SELECT CONCAT("Count: ", counter);        
END

运行存储过程返回以下结果:

+--------------------------+
|CONCAT("Count: ", counter)|
+--------------------------+
|                  Count: 1|
+--------------------------+

调试表中的结果是:

+------------+---------+-----------------------+
|iddebugTable|bigintval|                 strval|
+------------+---------+-----------------------+
|           1|     NULL|"transactionId is NULL"|
+------------+---------+-----------------------+

这意味着该值没有被复制

当运行 SQL 时(因为它在存储过程中)，它返回:

+-------------+
|transactionid|
+-------------+
|          591|
+-------------+

Answer 1

我发现了问题，它很奇怪。它不会导致任何错误和/或异常，只是不会将任何值放入变量中。解决方案是将游标声明语句从:

DECLARE txnEntryCur CURSOR FOR 
    SELECT 
        `transactionid`
    FROM 
        `transactionentry`
    LIMIT 1;

收件人:

DECLARE txnEntryCur CURSOR FOR 
    SELECT 
        `transactionentry`.`transactionid`
    FROM 
        `transactionentry`
    LIMIT 1;

甚至文档也没有表明它可能是个问题 (https://dev.mysql.com/doc/refman/5.7/en/declare-cursor.html)

如果我从多个表中进行选择，我只会完全限定 SQL 语句的 SELECT(和 WHERE)部分，因此不会在更复杂的查询中选择它。

我希望这会在将来为某人节省一些时间。