Question

我最初没有编写这段代码，但它确实曾经有效。不幸的是它不再有效了。我的研究表明它在SQL类型中是不匹配的，但我在SQL中不够精通修复错误。希望有人可以指导我。

SELECT DISTINCT (`users`.`card_id` ) AS `card_id2`
, `users` .`firstname` AS `First Name`
, `users`.`lastname` AS `Last Name`
, `users`.`card_id` AS `Card ID`
, `users`.`address1` AS `Address`
, `users`.`address2` AS `Address2`
, `users`.`city` AS `City`
, `users`.`state` AS `State`
, `users`.`zip` AS `Zip`
, `users`.`email` AS `Email`
, `users`.`phone_area`
, `users`.`phone_exchange`
, `users`.`phone_number`
, `trans`.`trans_dt` AS `Last Trans Date`
, `trans`.`credit_balance` AS `Credit Balance`
, `trans`.`balance` AS `Gift Balance`
, `users`.`gender` AS `Gender`
, `users`.`birthdate` AS `Birthday (Age)`
, `users`.`register_dt` AS `Registration Date`
, `merchants`.`company`
, `merchants`.`merchantkey`FROM `trans`
, `users`
, (SELECT `card_id`, max( `trans_id` ) AS `trans_dt` 
   FROM `trans` 
   WHERE `trans`.`trans_type` >0 GROUP BY `card_id`
) AS `trans_max` 
LEFT JOIN `merchants` ON `merchants`.`merchantkey`=`trans`.`merchantkey` 
WHERE trans.card_id = users.card_id 
AND trans.card_id = trans_max.card_id 
AND trans.trans_id = trans_max.trans_dt 
ORDER BY users.lastname, users.firstname;



Error Code: 1054. Unknown column 'trans.merchantkey' in 'on clause'

Answer 1

我复制并粘贴您的查询。 FROM子句位于错误的位置。 merchants.merchantkey和FROM trans之间没有空格。为什么在SELECT子句之后还有一些FROM子句，然后是LEFT JOIN？

SELECT DISTINCT ...
, `merchants`.`company`
, `merchants`.`merchantkey`FROM `trans`
, `users`
, (SELECT `card_id`, max( `trans_id` ) AS `trans_dt` 
   FROM `trans` 
   WHERE `trans`.`trans_type` >0 GROUP BY `card_id`
) AS `trans_max` 
LEFT JOIN `merchants` ON `merchants`.`merchantkey`=`trans`.`merchantkey`
...

我在想你的FROM不合适。尝试在FROM

之前移动LEFT JOIN子句

SELECT DISTINCT (`users`.`card_id` ) AS `card_id2`
    , `users` .`firstname` AS `First Name`
    , `users`.`lastname` AS `Last Name`
    , `users`.`card_id` AS `Card ID`
    , `users`.`address1` AS `Address`
    , `users`.`address2` AS `Address2`
    , `users`.`city` AS `City`
    , `users`.`state` AS `State`
    , `users`.`zip` AS `Zip`
    , `users`.`email` AS `Email`
    , `users`.`phone_area`
    , `users`.`phone_exchange`
    , `users`.`phone_number`
    , `trans`.`trans_dt` AS `Last Trans Date`
    , `trans`.`credit_balance` AS `Credit Balance`
    , `trans`.`balance` AS `Gift Balance`
    , `users`.`gender` AS `Gender`
    , `users`.`birthdate` AS `Birthday (Age)`
    , `users`.`register_dt` AS `Registration Date`
    , `merchants`.`company`
    , `merchants`.`merchantkey
    , `users`
    , (
        SELECT `card_id`, max( `trans_id` ) AS `trans_dt` 
        FROM `trans` 
        WHERE `trans`.`trans_type` >0 GROUP BY `card_id`
    ) AS `trans_max` 
FROM `trans`
LEFT JOIN `merchants` ON `merchants`.`merchantkey`=`trans`.`merchantkey`
WHERE trans.card_id = users.card_id 
    AND trans.card_id = trans_max.card_id 
    AND trans.trans_id = trans_max.trans_dt 
ORDER BY users.lastname, users.firstname;

Answer 2

错误表明您的merchantkey表中实际上没有trans字段。我认为你确实有这个领域，错误是由混合连接样式引起的。您已经弃用了ANSI-89样式（FROM tablea, tableb WHERE a.key = b.key）以及正确的ANSI-92样式（FROM tablea JOIN tableb ON a.key = b.key）。两者都独立工作，但混合它们会产生优先级问题，因为在ANSI-89样式连接之前评估ANSI-92样式连接。此优先级问题会导致错误，因为您引用了LEFT JOIN中尚未评估的字段。切换到所有正确的ANSI-92样式连接是很好的做法，并且应该修复您的错误：

SELECT DISTINCT (users.card_id ) AS card_id2
, users .firstname AS `First Name`
, users.lastname AS `Last Name`
, users.card_id AS `Card ID`
, users.address1 AS Address
, users.address2 AS Address2
, users.city AS City
, users.state AS State
, users.zip AS Zip
, users.email AS Email
, users.phone_area
, users.phone_exchange
, users.phone_number
, trans.trans_dt AS `Last Trans Date`
, trans.credit_balance AS `Credit Balance`
, trans.balance AS `Gift Balance`
, users.gender AS Gender
, users.birthdate AS `Birthday (Age)`
, users.register_dt AS `Registration Date`
, merchants.company
, merchants.merchantkey
FROM trans 
JOIN users 
  ON    trans.card_id = users.card_id 
JOIN (SELECT card_id
            , max( trans_id ) AS trans_dt
      FROM trans
      WHERE trans.trans_type > 0 
      GROUP BY card_id
    ) AS trans_max
  ON    trans.card_id = trans_max.card_id 
   AND  trans.trans_id = trans_max.trans_dt  
LEFT JOIN merchants 
  ON     merchants.merchantkey = trans.merchantkey  
ORDER BY users.lastname, users.firstname;

MySql文档：http://dev.mysql.com/doc/refman/5.7/en/join.html

以前，逗号运算符（，）和JOIN都有相同的含义优先级，因此连接表达式t1，t2 JOIN t3被解释为（（t1，t2）JOIN t3）。现在JOIN具有更高的优先级，所以表达式被解释为（t1，（t2 JOIN t3））。此更改会影响语句使用ON子句，因为该子句只能引用列在连接的操作数中，优先级的变化会发生变化解释这些操作数是什么。

看起来这个优先级问题并不总是存在，但它可能已经在MySQL 5.7中引入了，所以如果查询以前有效，那么它可能是以前在早期版本上运行的。

以下SQL语句用于工作，但现在我收到一个我知道存在的列的未知列错误

2 个答案: