mysql报错Expression #3 of SELECT list is not in GROUP BY clause and contains nonaggregated column问题

2022-09-22 14:43:22

今天sql一对多关联查询发现一个错误，提示说查询的字段不在group by的子句中，因为sql_mode是only_full_group_by。

报错信息：

#1055 - Expression #3 of SELECT list is not in GROUP BY clause and contains nonaggregated column ‘xt_sc.t_comment.content‘ which is not 
functionally dependent on columns in GROUP BY clause; this is incompatible with sql_mode=only_full_group_by

执行的sql语句

SELECT 
    n.id,
    n.title,
    n.qq,
    u.username,
    c.content,
    c.create_time 
FROM 
    `t_need` AS `n` 
LEFT JOIN `t_users` `u` ON `n`.`user_id`=`u`.`id` 
INNER JOIN ( SELECT max(id) as id,n_id,content,create_time FROM `t_comment` GROUP BY `n_id` ) AS `c` ON `n`.`id`=`c`.`n_id` 
WHERE  `n`.`status` = 2  AND `n`.`form` = 1
GROUP BY `n`.`id` 
ORDER BY `stick` DESC,`n`.`update_time` DESC 
LIMIT 0,30

问题出现的原因：
MySQL 5.7.5及以上功能依赖检测功能。如果启用了ONLY_FULL_GROUP_BY SQL模式（默认情况下），MySQL将拒绝选择列表，HAVING条件或ORDER BY列表的查询引用在GROUP BY子句中既未命名的非集合列，也不在功能上依赖于它们。（5.7.5之前，MySQL没有检测到功能依赖关系，默认情况下不启用ONLY_FULL_GROUP_BY。有关5.7.5之前的行为的说明，请参见“MySQL 5.6参考手册”。）

查看mysql本地的sql_mode命令：

select @@sql_mode;
show variables like ‘sql_mode‘;

输出sql_mode的值：ONLY_FULL_GROUP_BY,STRICT_TRANS_TABLES,NO_ZERO_IN_DATE,NO_ZER
_DATE,ERROR_FOR_DIVISION_BY_ZERO,NO_AUTO_CREATE_USER,NO_ENGINE_SUBSTITUTION

确实第一个是only_full_group_by，这个模式说明对于GROUP BY聚合操作，如果在SELECT中的列，没有在GROUP BY中出现，那么将认为这个SQL是不合法的，因为列不在GROUP BY从句中。就是说不允许select的列没有出现在group by的子句中。

在5.7.5以上，sql的默认模式配置是ONLY_FULL_GROUP_BY。

解决办法1：
简单粗暴的解决方法是删除ONLY_FULL_GROUP_BY，不推荐
在数据库控制台输入命令：SET GLOBAL sql_mode=(SELECT REPLACE(@@sql_mode,‘ONLY_FULL_GROUP_BY‘,‘‘));

然后再执行查询语句，可以正常查询出结果

解决办法2：

优化sql语句

SELECT 
    n.id,
    n.title,
    n.qq,
    u.username,
    c.content,
    c.create_time 
FROM 
    `t_need` AS `n` 
LEFT JOIN `t_users` `u` ON `n`.`user_id`=`u`.`id` 
INNER JOIN ( 
    SELECT a.id,a.n_id,a.content,a.create_time FROM `t_comment` AS `a`
    LEFT JOIN(
        SELECT max(id) as id,n_id FROM `t_comment` GROUP BY `n_id` 
    ) AS `b` ON `b`.`n_id`=`a`.`n_id` 
    WHERE `a`.`id` = `b`.`id`
) AS `c` ON `n`.`id` = `c`.`n_id`
WHERE  `n`.`status` = 2  AND `n`.`form` = 1
GROUP BY `n`.`id` 
ORDER BY `stick` DESC,`n`.`update_time` DESC 
LIMIT 0,30

执行以上查询语句，可以正常查询出结果。

done!

mysql报错Expression #3 of SELECT list is not in GROUP BY clause and contains nonaggregated column问题

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