Mysql 我的查询中的分组错误

我想知道是否有人能解释一下下面的错误。sql在本地运行良好，但我在远程收到以下错误

SQL查询：

$inQ = "
    SELECT category.category_name, GROUP_CONCAT(subject.subjects SEPARATOR ', ') AS subjects
    FROM category 
    INNER JOIN tutor_category_subject ON tutor_category_subject.category_id = category.category_id
    INNER JOIN subject ON tutor_category_subject.subject_id = subject.subject_id
    WHERE tutor_category_subject.tutor_id = $tutorId AND tutor_category_subject.category_id = $categoryId
"; 

MySQL说：

#1140-如果没有GROUP BY子句，则在没有GROUP列的情况下混合GROUP列（MIN（）、MAX（）、COUNT（）、…）是非法的

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正如错误所说：如果没有GROUPBY子句，就不能混合group列和非group列。尝试添加一个：

SELECT category.category_name, GROUP_CONCAT(subject.subjects SEPARATOR ', ') AS subjects
FROM category 
INNER JOIN tutor_category_subject ON tutor_category_subject.category_id = category.category_id
INNER JOIN subject ON tutor_category_subject.subject_id = subject.subject_id
WHERE tutor_category_subject.tutor_id = $tutorId AND tutor_category_subject.category_id = $categoryId
GROUP BY category.category_name

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我相信你想要这个：

SELECT category.category_name, GROUP_CONCAT(subject.subjects SEPARATOR ', ') AS subjects
FROM category 
  INNER JOIN tutor_category_subject ON tutor_category_subject.category_id = category.category_id
  INNER JOIN subject ON tutor_category_subject.subject_id = subject.subject_id
WHERE tutor_category_subject.tutor_id = $tutorId AND tutor_category_subject.category_id = $categoryId
GROUP BY category.category_name, subject.subjects

您需要添加

groupby

子句，以使您的select能够使用

GROUP\u CONCAT