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Hello All,

I want to design database for my application. In my application users are allowed to create category, subcategory and their attributes. One SubCategory can have more than one attribute of different datatypes. User will select CategoryID,SubCategoryID and add value to its attribute(s). So,I am planning to create different tables for different attributes because i don't want to change main table every time if new attribute created. Two things
i)Create attribute table dynamically
ii)Dynamically DML query in attribute table.
So, relationship will be with CategoryID, SubCategoryID as

CategoryId SubCategoryID

CategoryID SubcategoryID AttributeValue

So everytime I will writing dynamic queries for insert and create.
Do you think this is fine? If you have any other ideas then let me know.
PIEBALDconsult 14-Jul-14 11:26am
"Do you think this is fine?"

I don't; it sounds like a maintenance nightmare. If you are using Sql Server, have you considered using XML to hold the "attributes"?

What more information can you provide? Any examples of a Category or SubCategory table?

You are trying to badly deviate from relational model. At the same time, all your problems are simply resolved in the relational model. First, let's start from the notion of "sub-category". You can have just one table "Category" with the key "Id". If you add the columns "ParentCategory" which carries the IDs of the categories parent in relation to the category of the current record, you will have the tree of arbitrary depth built on the base of the parent-child relationships between categories.

The rest of it depends on what on what the attribute should be and what "different attributes" may mean. You never need to create a table dynamically. "Different attributes" does not mean different types. So, you can have only one table for all attributes, and they will be different, because the attribute's attributes are different (different values in some or all columns). But let's suppose you have different types of attributes, which means that you have different set of columns for each table. Now, it depends on where those types come from. If the attribute types are known in advance, you need to have a separate attribute table per attribute type, so the problem is reduced to a previous one.

And finally, let's consider the case when you need to create a new attribute type dynamically. It simply means that the type should be represented not as the type of the table, but become a data type. The most basic approach is this: create one new table of dynamic attributes. It can have, say, name, value, and, importantly, a column "owner" with the foreign key pointing to the attribute object. That said, you can have the object "attribute" each having unlimited number of "dynamic attributes".

Please see:[^],[^],[^].

Maciej Los 14-Jul-14 15:24pm
+5! Valuable answer.
I think OP wants to create databse for hierarchical data. Please, look at my answer.
Sergey Alexandrovich Kryukov 14-Jul-14 15:55pm
Thank you, Maciej.
Hierarchical data is just the special case of the approach to supporting of some object graphs in relational model I tried to explain...
Maciej Los 14-Jul-14 17:37pm
I'd suggest you to read about recursive hierarchies[^].

You should have only 2 tables:
Parent INT (related to CatID)
CatName NVARCHAR(50)
... (other fields)

CatID INT (related to CatId in Categories table)

Sample Data:
CatId    Parent    CatName
1        0         MainCat
2        1         MainCatSubCat1
3        1         MainCatSubCat2
4        2         SubCat1SubSubCat1
5        4         SubCat1SubSubCat1SubCat1

Its "visual" representation diagram:
|   |
|   +---4
|       |
|       +---5

Do you get it now?
Sergey Alexandrovich Kryukov 14-Jul-14 15:56pm
Useful explanation, my 5.
Look, at the new comment to your comment to my answer though.
Maciej Los 14-Jul-14 17:37pm
Thank you, Sergey ;)

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