Question

表项目：pid（pk），名称...
表类别：pid（pk），project（项目的pid），parent（其他类别的pid）...
表计数：项目（项目的pid），类别（类别的pid），计数...

我之前使用过此查询

SELECT
categories.*, projects.pid, projects.name, parent_category.*
FROM categories
INNER JOIN projects ON projects.pid = categories.project
LEFT JOIN categories AS parent_category ON parent_category.pid = categories.parent

效果很好

这次，我们需要SUM，COUNT个数据。所以我添加了“ counts”表并进行了查询。

SELECT
categories.*, projects.pid, projects.name, SUM(counts.count), COUNT(counts.count),
parent_category.*, SUM(parent_category_count.count), COUNT(parent_category_count.count)
FROM categories
INNER JOIN projects ON projects.pid = categories.project
LEFT JOIN counts ON counts.category = categories.pid
LEFT JOIN categories AS parent_category ON parent_category.pid = categories.parent
LEFT JOIN counts AS parent_category_count ON parent_category_count.category = categories.pid

然后我得到

错误：聚合函数调用无法嵌套

我该怎么办？这个查询基本上有意义吗？还是应该拆分？

Answer 1

您应该添加适当的GROUP BY子句（在您的情况下应为Categories.pid）

    SELECT
    categories.*
    , projects.pid
    , projects.name
    , SUM(counts.count)
    , COUNT(counts.count)
    , parent_category.*
    , SUM(parent_category_count.count)
    , COUNT(parent_category_count.count)
    FROM categories
    INNER JOIN projects ON projects.pid = categories.project
    LEFT JOIN counts ON counts.category = categories.pid
    LEFT JOIN categories AS parent_category ON parent_category.pid = categories.parent
    LEFT JOIN counts AS parent_category_count ON parent_category_count.category = categories.pid
    GROUP BY categories.pid

或根据您的评论

    SELECT
    categories.*
    , projects.pid
    , projects.name
    , SUM(counts.count)
    , COUNT(counts.count)
    , parent_category.*
    , SUM(parent_category_count.count)
    , COUNT(parent_category_count.count)
    FROM categories
    INNER JOIN projects ON projects.pid = categories.project
    LEFT JOIN counts ON counts.category = categories.pid
    LEFT JOIN categories AS parent_category ON parent_category.pid = categories.parent
    LEFT JOIN counts AS parent_category_count ON parent_category_count.category = categories.pid
    GROUP BY categories.pid, projects.pid, parent_category.pid

可以将聚合函数与join一起使用吗？

1 个答案: