Mysql Query Incorporating Self Referential Join

Question

Say I have four tables:

------------- features --------------
id: int
name: varchar
-------------------------------------

-------- feature_categories ---------
feature_id: int
category_id: int    
-------------------------------------

----------- categories --------------
id: int
name: varchar    
-------------------------------------

------ category_subcategories -------
category_id: int
sub_category_id: int    
-------------------------------------

category has many (sub)categories, through self referential join subcategories

A feature has many categories, of those some will be subcategories, through join feature_categories

What I need is to send an array of feature ids and a (main) category id and have returned all subcategories. This is proving more difficult than I would have hoped so I'd appreciate greatly any help. Let me know if this question isn't clear.

EDIT I don't need the feature table to be included in any query. In facet, I only require the subcategory (category) name field to be returned.

Answer 1

does the following do the job?

SELECT *
FROM `category_subcategories` sc
  JOIN `categories` c ON sc.category_id = c.id
  JOIN `feature_categories` fc ON fc.category_id = c.id
WHERE fc.feature_id IN (0,1,2,...)
  AND c.id = main_category_id;

Answer 2

select f.name featureName,
  c.name CategoryName,
  sc.name SubCategoryName 
from features f
join features_categories fc on f.id=fc.feature_id
join categories c on fc.category_id=c.id
join category_subcategories cs on c.id=cs.category_id
join categories sc on cs.sub_categories_id=sc.id
WHERE f.id IN (0,1,2,...)

If I understand correctly what you are asking...

Answer 3

Had to work through this a bit, but either below should work. 2nd one is probably more efficient:

 select f.name featureName, 
  c.name CategoryName, 
  c2.name SubCategoryName  
    FROM features f, feature_categories fc, categories c, category_subcategories sc, categories c2, feature_categories fc2
    WHERE f.id = fc.feature_id
    AND c.id = fc.category_id
    AND sc.category_id = c.id
    and c2.id = sc.sub_category_id
    and fc2.category_id = c2.id
    AND f.id in (0,1,2,...)
    and fc2.feature_id in (0,1,2,...)
    AND c.id = @main_category_id

or:

    select f.name featureName, 
  c.name CategoryName, 
  c2.name SubCategoryName  
        FROM features f 
        inner join feature_categories fc on f.id = fc.feature_id
        inner join categories c on c.id = fc.category_id
        inner join category_subcategories sc on sc.category_id = c.id
        inner join categories c2 on c2.id = sc.sub_category_id
        inner join feature_categories fc2 on fc.category_id = c2.id

        WHERE f.id in (0,1,2,...)
        AND c.id = @main_category_id

        and fc2.feature_id in (0,1,2,...)

Answer 4

select f.name featureName, 
c.name CategoryName, 
c2.name SubCategoryName  
FROM features f 
inner join feature_categories fc on f.id = fc.feature_id
inner join categories c on c.id = fc.category_id
inner join category_subcategories sc on sc.category_id = c.id
inner join categories c2 on c2.id = sc.sub_category_id
inner join feature_categories fc2 on fc.category_id = c2.id and fc2.feature_id = fc.feature_id
WHERE f.id in (0,1,2,...)
AND c.id = @main_category_id;

Answer 5

This may give expected result

SELECT    cat.name
FROM       categories cat,
                 feature_categories feacat,
                 category_subcategories cat_subCat
WHERE     feacat.feature_id in (1,2,3)
AND          feacat.category_id = cat.id
AND         exists(select 1 from cat_subCat WHERE category_id = @CatID and sub_category_id=cat.id)