我正在关注这个问题的答案: MySQL:是否可以对多行进行分组连接?
但是我遇到了 MySql 错误:
.#1054 - Unknown column 'CM_Cocktail.id' in 'field list'
当我删除这个 CM_Cocktail.id 内容时,会出现下一个错误:
#1054 - Unknown column 'CM_Zutat.name' in 'field list'
。我尝试使用别名,但情况变得更糟......也许我是盲目的。
SELECT
CM_Cocktail.id, CM_Cocktail.name,
GROUP_CONCAT(CM_Zutat.name SEPARATOR ', ')
FROM (
SELECT CM_Cocktail.id, CM_Cocktail.name AS cname, CM_Zutat.name
FROM CM_Cocktail, CM_CocktailHatZutat, CM_Zutat
WHERE CM_Cocktail.id=CM_CocktailHatZutat.cocktail_id
AND CM_CocktailHatZutat.zutat_id=CM_Zutat.id
) group_attr
GROUP BY CM_Cocktail.id;
CREATE TABLE IF NOT EXISTS `CM_Cocktail` (
`id` int(3) NOT NULL AUTO_INCREMENT,
`name` varchar(255) NOT NULL,
PRIMARY KEY (`id`),
UNIQUE KEY `name` (`name`)
) ENGINE=MyISAM DEFAULT CHARSET=latin1 AUTO_INCREMENT=4 ;
CREATE TABLE IF NOT EXISTS `CM_CocktailHatZutat` (
`cocktail_id` int(3) NOT NULL,
`zutat_id` int(3) NOT NULL,
`zutat_menge` int(4) NOT NULL
) ENGINE=MyISAM DEFAULT CHARSET=latin1;
CREATE TABLE IF NOT EXISTS `CM_Zutat` (
`id` int(3) NOT NULL AUTO_INCREMENT,
`name` varchar(255) NOT NULL,
PRIMARY KEY (`id`),
UNIQUE KEY `name` (`name`)
) ENGINE=MyISAM DEFAULT CHARSET=latin1 AUTO_INCREMENT=3 ;
您需要在子查询中定义列别名,然后使用别名作为父字段,如下例所示:
SELECT
CocktailID, cname,
GROUP_CONCAT(ZName SEPARATOR ', ')
FROM (
SELECT CM_Cocktail.id as CocktailID, CM_Cocktail.name AS cname, CM_Zutat.name as ZName
FROM CM_Cocktail, CM_CocktailHatZutat, CM_Zutat
WHERE CM_Cocktail.id=CM_CocktailHatZutat.cocktail_id
AND CM_CocktailHatZutat.zutat_id=CM_Zutat.id
) group_attr
GROUP BY CocktailID;
请尝试这个
SELECT
id, name,
GROUP_CONCAT(CM_Zutat.name SEPARATOR ', ')
FROM (
SELECT CM_Cocktail.id, CM_Cocktail.name AS cname, CM_Zutat.name
FROM CM_Cocktail, CM_CocktailHatZutat, CM_Zutat
WHERE CM_Cocktail.id=CM_CocktailHatZutat.cocktail_id
AND CM_CocktailHatZutat.zutat_id=CM_Zutat.id
) group_attr
GROUP BY id;
因为你使用子查询
该错误通常是因为新列添加到实体中并且 hibernate 无法更新实体。要解决此问题,请在 application.properties 或 application.yaml 文件中,将 hibernate ddl 从 update 更改为 create-drop
jpa:
database: MYSQL
hibernate:
ddl-auto: create-drop
注意:这不应该在生产中完成,因为它会清除数据库。