Laravel Query Builder 从加入计数
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Laravel Query Builder count from join
提问by Coffee
So in my database I have table called website_tags, which contains id, titleand so on, and also I have table called websites, with similar construction. And also there is table called assigned_tags, which contains relation between tags and websites, so it contains relation id, tag_id and website_id.
所以在我的数据库中，我有一个名为 的表website_tags，其中包含id, title等等，还有一个名为 的表websites，具有类似的结构。还有一个叫做 的表assigned_tags，它包含标签和网站之间的关系，所以它包含关系id, tag_id and website_id。
What I need is to join these tables with query, I need to get all the tags and count how many times these tags are used. So, for example website_tags contains following information:
我需要的是将这些表与查询连接起来，我需要获取所有标签并计算这些标签的使用次数。因此，例如 website_tags 包含以下信息：
1: men
2: women
And assigned tags contains like id: tag_id: website_id
并且分配的标签包含像 id: tag_id: website_id
1: 1: 1
2: 1: 2
3: 2: 2
So I will get that tag 'men' is used in 2 websites and tag 'women' is used in 1. How should I build the query?For now I have:
因此，我将在 2 个网站中使用标签“男性”，在 1 个网站中使用标签“女性”。我应该如何构建查询？现在我有：
DB::table('website_tags')
->join('assigned_tags', 'website_tags.id', '=', 'assigned_tags.tag_id')
->select('website_tags.id as id', 'website_tags.title as title', DB::raw("count(assigned_tags.tag_id) as count"))-
>get();
But this is wrong, this query just counts rows in assigned_tags.
但这是错误的，这个查询只计算assigned_tags 中的行数。
回答by KuKeC
You have to define groupByso query will know how to count it (just like in the regular SQL)
您必须定义，groupBy以便查询知道如何计算它（就像在常规 SQL 中一样）
Try something like this
尝试这样的事情
DB::table('website_tags')
->join('assigned_tags', 'website_tags.id', '=', 'assigned_tags.tag_id')
->select('website_tags.id as id', 'website_tags.title as title', DB::raw("count(assigned_tags.tag_id) as count"))
->groupBy('website_tags.id')
->get();
