I've got a table (something similar to)

product: id, name, type
product_type: id, name, group_id
product_group: id, name

This model is working OK, I built a question that joins tables in order to request to obtain all items which has product group 14 or type 12..

Now i'm facing an problem, I have to increase the types to some product.

product: id, name, type, type_1, type_2, type_3
product_type: id, name, group_id
product_group: id, name

Following this I've written a question that may retrieve type=12 or type_1=12 or type_2=12 but I don't understand how to write a question which will retrieve if group=14 or group_1=14.

My totally:

SELECT product.*,  
       product_group.group_name 
FROM product,
     product_group,
     product_type 
WHERE product.product_type = product_type.id 
  AND product_group.id = product_type.product_group 
  AND product_group=14

How do i add:

(... or product_group_1=14 or product_group_2=14)

Thank for just about any help, here's some example

- product: id=2, name=cleaning kit, type=6 (photo accessorioes), type_1=9 (video accessorioes), type_2=33 (cleaning supply)
---------------------------------
- type: id=6, name=photo accessorioes, group=12 (photo equipment)
- type: id=9, name=video accessorioes, group=14 (video equipment)
- type: id=33, name=cleaning supply, group=31 (some group)
---------------------------------
- group: id=12, name=photo equipment
- group: id=14, name=video equipment
- group: id=31, name=some group

Now I have to find all product which have been in group 14 for instance.

You might like to re-think your model. If you start naming posts _1, _2, _3 etc it's frequently an indication that the schema is not normalised. What's different between your different kinds for any product? Would you introduce a join table such as this: product_types: product_id, type_id

EDIT It may sound like there are many-to-many associations (i.e. each product might have several group, each group might have several product). To do this inside a relational DB like MySQL you'll need a table to become listed on your items for your groups such as this:

product_groups: product_id, group_id

After that you can query for those items inside a group by JOINing on that table while using relevant group_id.

EDIT In line with the example data you provided I'd restructure your schema such as this

product: id=2, name=cleaning kit, 
---------------------------------
product_types: product_id=2, type_id=6 
product_types: product_id=2, type_id=9
product_types: product_id=2, type_id=33
---------------------------------
type: id=6, name=photo accessorioes, group=12 (photo equipment)
type: id=9, name=video accessorioes, group=14 (video equipment)
type: id=33, name=cleaning supply, group=31 (some group)
---------------------------------
group: id=12, name=photo equipment
group: id=14, name=video equipment
group: id=31, name=some group

The merchandise_types table will be a join table having a multi-column primary key on product_id and kindidentification. These posts are foreign secrets relevant to product.id and kind.identification correspondingly.