PHP - 递归地从SQL数据库获取数据

Question

I have 2 tables tl_docs_categories which are the parent table for tl_docs. Structure of tables is:

tl_docs_categories
[
   id,
   category_name,
   pid (give the posibility to create subcategories / pid = tl_docs_categories.id if have subcategory)
]
tl_docs
[
   id,
   doc_name,
   doc_url,
   pid(id for category)
]

So I have something like this in my database:

What I want is to return all result when I select category which is in red, I want to return all documents and subcategories names, in my view I use a select form to return the id of selected parent category in red.

Here is my php function :

public function checkSQL($id)
{
    if(!empty($id))
    {
        /* SQL CHECK IF HAVE DOCS */
        $sqlDoc = "SELECT category_name, doc_name, doc_url FROM tl_docs_categories dc
                   LEFT JOIN tl_docs d ON dc.id = d.pid WHERE d.pid = " . $id;
        $objDocs = Database::getInstance()->query($sqlDoc);
        if ($objDocs->numRows == 0)
        {
            /* SQL CHECK IF HAVE CHILD */
            $sqlChild = "SELECT dc.id, category_name, doc_name, doc_url FROM tl_docs_categories dc
                         LEFT JOIN tl_docs d ON dc.id = d.pid WHERE dc.pid =" . $id;
            $objDocs = Database::getInstance()->query($sqlChild);
                return $objDocs;
            }
        }
        else
        {
            return $objDocs;
        }
    }
}

I'm a bit lost and I don't have a solution to do it recursively and return datas for each category, subcategory, subsubcategory and more then.

Thank you for your help in advance.

Answer 1

I'm not sure about the syntax, but the idea is to call checkSQL on each level, if you want to return all results, then you have to adapt the $objDocs var to be an array.

public function checkSQL($id)
{
    if(!empty($id))
    {
        /* SQL CHECK IF HAVE DOCS */
        $sqlDoc = "SELECT category_name, doc_name, doc_url FROM tl_docs_categories dc
                   LEFT JOIN tl_docs d ON dc.id = d.pid WHERE d.pid = " . $id;
        $objDocs = Database::getInstance()->query($sqlDoc);

        if ($objDocs->numRows > 0) {
            foreach ($objDocs->fetchColumn() as $row) {
                $objDocs = $this->checkSQL($row->id);
            }
        }

        return $objDocs;
    }

    return null;
}