Question

I have a category table

cat_id, cat_name, parent_id, cat_slug

and I have article table as follow

art_id, cat_id, art_title, art_content, author_id .....

and my users table as

user_id, username, pw, .....

so with these data, I want to display all articles which are listed under sub category

for example:

url of main category is: mydomain.com/cat/business
url of sub category is: mydomian.com/cat/business/advertising

so when people visit the main category, then it should display the subcategories listed articles on main category even though the cat_id is not mentioned as main category. I want to list out all sub categories of business’s subcategories articles on business category page.

what is the query, i should try to achieve this

help will be appreciated. thanks

Answer 1

First, to get your categories…

If your category nesting is only two levels deep (parent and child) or you are only interested in direct sub-categories (i.e. not subcategories of subcategories), then your SQL is pretty simple:

SELECT cat_id FROM category_table WHERE cat_id = $catid OR parent_id = $catid

If your nesting is deeper, then you’ll need to recursively query as far down as your category nesting goes. For example, if you limit yourself to 3 levels, you can do this with SQL like this:

SELECT cat_id FROM category_table ct1
WHERE cat_id = $catid OR parent_id = $catid
OR parent_id in (SELECT cat_id FROM category_table WHERE parent_id = ct1.cat_id)

Similarly, for a 4-level deep nesting, you can make the SQL even more complicated:

SELECT cat_id FROM category_table ct1
WHERE cat_id = $catid OR parent_id = $catid
OR parent_id in (SELECT cat_id FROM category_table ct2 WHERE parent_id = ct1.cat_id
                 OR parent_id in
                 (SELECT cat_id FROM category_table ct3 WHERE parent_id = ct2.cat_id))

And so on.

If you do not have a fixed nesting depth, then you’ll need to do the looping in the code.

Once you have all categories, then you query articles. So for a simple 2-level dependency, you’ll get

SELECT * FROM article_table
WHERE cat_id in (SELECT cat_id FROM category_table WHERE cat_id = $catid OR parent_id = $catid)

Similarly, for a 3-level nesting, you’ll get

SELECT * FROM article_table
WHERE cat_id in
    (SELECT cat_id FROM category_table ct1
     WHERE cat_id = $catid OR parent_id = $catid
     OR parent_id in (SELECT cat_id FROM category_table WHERE parent_id = ct1.cat_id))

And so on…