针对其他表中每个id的rown计数包含与使用活动记录的外键相同的id

Question

我有下面两张桌子，在这里我需要完整的机架列表，并计算与机架.id和机架ID匹配的外键编号，机架ID与应与机架ID匹配的机架不匹配0

语气

function getRacksList()
    {
        $this->db->select('rack.name as name, rack.details as details, rack.id as id');
        $this->db->from('books');
        $this->db->join('rack', 'rack.id = books.rack_id', 'left');
        $query = $this->db->get();

        return $query->result();
    }

Controller
 function rackDetails(){

        $data['racks'] = $this->rack_model->getRacksList();

        print_r($data['racks']);
        die();
    }

我得到的结果

Array ( [0] => stdClass Object ( [name] => Software Engineering [details] => This Book Rack is for Software Engineering Books [id] => 1 )
 [1] => stdClass Object ( [name] => Computer Sciences [details] => This rack is for Computer Sciences Books [id] => 2 ) 
[2] => stdClass Object ( [name] => Software Engineering [details] => This Book Rack is for Software Engineering Books [id] => 1 ) 
[3] => stdClass Object ( [name] => Software Engineering [details] => This Book Rack is for Software Engineering Books [id] => 1 ) 
)

架

id    rack_name
1     rack one
2     rack two
3     rack three
4     rack four
5     rack five

图书

id    book_name   rack_id
1     book one      1
2     book two      1
3     book three    2
4     book four     2
5     book five     3

Answer 1

如果我正确地遵循了您的要求，一种解决方案是将rack表与rack表一起LEFT JOIN books表，并使用聚合来计算每个书架中有多少书。

这是一个使用原始sql的代码片段：

function getRacksList()
{
    $query = $this->db->query("
        SELECT rack.name, rack.details, rack.id, COUNT(books.rack_id) as books_count
        FROM rack
        LEFT JOIN books ON rack.id = books.rack_id
        GROUP BY rack.name, rack.details, rack.id
    ");
    return $query->result();
}