Question

I have a table named size here, something like this:

size id | size name 
   1            S
   2            M
   3            L
   4            XL

But I am confused when I found that the size must have any category, I mean something like cloth_size, pant_size, sheets_size. That would be different. Row will be 6XL, 5XL, 4XL. I think I should crate the table sheets_size like:

size id size name 
1            S
2            M
3            L
4            XL
5            XXL

or should I create the table category like:

category_id category_name
1              cloth
2              dress
3              pants
4              sheets

table size:

size id | size name   | category
1            S              1
2            M              1
3            L              1
4            XL             1  
5            XXL            4

Which one better?

Answer 1

I believe the best and easiest method is to have a table with all categories, like you described:

category_id  |   category_name
    1        |      cloth
    2        |      dress
    3        |      pants
    4        |      sheets

and then have a table with all sizes (from S to 6XL)

   size id   |   size name 
      1      |       S
      2      |       M
     ...     |      ...
      10     |      6XL

These two tables will be in a many-to-many relationship since one category can have many sizes and one size can belong to many categories. This means that you will need a third table to hold the primary keys of each table.

   category_id   |   size_id
        1        |      1
        1        |      2
       ...       |     ...

This basically translates to category 1, has sizes 1 and 2, as in cloth has sizes S and M.