Question

我有这个问题：

SELECT
    course_category.id      AS languageId,
    course_category.code    AS languageCode,
    course_category.name    AS languageName,
    (
        SELECT
            SUM(gradebook_result.score)
        FROM
            gradebook_result
        JOIN
            gradebook_evaluation ON  gradebook_evaluation.id=gradebook_result.evaluation_id
        JOIN
            gradebook_category ON gradebook_category.id=gradebook_evaluation.category_id
        WHERE
            gradebook_category.course_code=course_category.code

    ) AS languageWordsTranslated
FROM
    course_category
WHERE
    course_category.code != 'GEN'
ORDER BY
    name
ASC

问题发生在嵌套的SELECT中，我在SELECT行上引用了course_category表时出错：

WHERE
    gradebook_category.course_code=course_category.code

给出错误：

Unknown column 'course_category.code' in 'where clause'

我之前使用其他项目完成了此查询，唯一的区别是此内容已加入其中。有什么想法吗？

编辑：我删除了连接并硬编码：

WHERE
    course_category.code = 'ARA'

似乎连接混乱，任何方法来解决这个问题？

Answer 1

尝试以不同的方式使用子查询并加入它：

SELECT
    course_category.id      AS languageId,
    course_category.code    AS languageCode,
    course_category.name    AS languageName,
    t.total AS languageWordsTranslated
FROM
    course_category
JOIN (
    SELECT gradebook_category.course_code, SUM(gradebook_result.score) as total
    FROM gradebook_result
    JOIN gradebook_evaluation ON  gradebook_evaluation.id=gradebook_result.evaluation_id
    JOIN gradebook_category ON gradebook_category.id=gradebook_evaluation.category_id
    GROUP BY gradebook_category.course_code
) t ON t.course_code = course_category.code
WHERE
    course_category.code != 'GEN'
ORDER BY
    name
ASC

MySQL嵌套选择引用外表？

1 个答案: