I am totally confused to store category and product data stored in the same table in hierarchical relation/Parent-child relation use in a table or if we create two separate table for category and product table?
in above table, i used the same table for storing category and product with parentId and childId, If we use like this then what benefits? Or we use a separate table for category and product and why? Please anyone help me
This really depends on if the relationship between store and product categories are one to many or many to many and if a single category can only belong to one category tree.
If the relationship is one to many, and a category can only belong to one tree, then you'll be able to use a single table, with a foreign key referencing the same table.
Otherwise, you'll likely be looking 2 or 3 tables. At a minimum you'll need one table for your categories, and then another for you relationship (what's known as a composite key table).
Also, if Product categories and Store Categories are inherently different (hold different data) then you should be using separate tables for them anyway.
Related
So I'm taking a look at the well-known Chinook DB. The PlaylistTrack table is obviously an association table because it just contains keys from two tables.
But what I don't quite understand is why certain other tables like Invoice are not association tables despite also containing at least two keys. Invoice, for example, contains InvoiceId and CustomerId (as well as some other fields).
I know that InvoiceId is the primary key for the invoice table and CustomerId is a foreign key pointing to another table. But isn't that the same for the PlaylistTrack table?
Conceptually speaking, what is it about the PlaylistTrack table that makes it an association table? And what is it that is different about the Invoice table that doesn't make it an association table? Or is it an association table?
It is because that it is a many-many relationship, all the other relationships are one-many.
A one-many relationship can be achieved by the child storing a unique reference/map association with it's ONE and ONLY parent (the parent potentially have 0-MANY children).
However, this embedding of the reference will not facilitate, the playlist track as a track can be in many playlists (so a track could have many parents). That is where the association tables comes in, it caters for many-many relationships (by that nature if can obviously also cater for one-one relationships).
However, I believe that the InvoiceLine table is also an associative table but with additional values (Unit price and Quantity) specific to the actual association/relationship.
I have a Product and a Product Category.
I can define a Product has Product Category relationship, or Product Category has Product.
Both make sense to me. My aim is to achieve a grouping of products to categorize them more easily. I see Product Category as a helper concept and not a concrete concept. i.e. a Product is something I could sell, something I can place into a shopping cart, etc. I cannot do that with a Product Category. But I can use it to group things, i.e. show a listing of Productthat belongs to a certain Product Category.
Many to Many relation is symmetrical, I assume, and there are two ways to create it. How can I determine which direction is correct in my case? Is there one?
Since many-to-many is bidirectional, there really is no need for consideration of a "correct direction". As for the design, I would create product_category as a static table with only primary keys; the products table with its own primary key column(s) such as Product ID; and a third association table which foreign keys the primary keys from the two tables.
PRODUCT_TAGS
PROD_ID|CAT
21|Heating
21|Security
25|Heating
37|Lighting
37|Security
I think you have a one-to-many relationship instead of a many-to-many.
Whenever I look at relationships of any type, I ask myself a question about the tables (using your table names):
Does a product have many categories, or does a category have many products?
If the first point is true, then the ID from the product table goes into the category table. Otherwise, the ID from the category table goes into the product table.
If both is true (a product has many categories and a category has many products), then you'll need a joining table.
I'm assuming that a category has many products, but a product can only have one category. If that's true, you would add a category_id to your product table.
If it's a many-to-many relationship, your table would look like this:
product_category_map (product_id, category_id)
Hope that answers your question. I recently wrote an article on normalisation that covers the concept of one-to-many and many-to-many relationships as it can be a confusing concept. (Disclosure: I own that website).
I found a schema in Google Images (see below) that can illustrate a problem I having in my data warehouse design:
My design is different, but this is the simplest figure I could find to convey my question, which is given the figure, I'm wondering how could the schema accommodate the following scenario: if a product had a unique number assigned to it by the SalesOrg (salesOrg_product_number)...For example, a salesOrg sells food items and assigns all food items of the same kind the same unique salesOrg_product_number. A different salesOrg would have a different salesOrg_product_number for that type of product.
I'm inclined to place the salesOrg_product_number attribute in the Product dimension table, but part of me thinks it should be in the salesOrg dimension table instead. I'm wondering which one of these is correct way in a data warehouse (not relational db) design to maintain the star schema?
In a perfect world the Primary Keys of a dimension table should be just surrogate key, without any meaning for the business. Table IDs should be invisible for the final users, but business code should be of course available.
A possible solution would be to have a product table with a structure like:
Product_id
Product_desc
Product_SO1_number
Product_SO2_number
...
Of course this will require to show the correct field to the correct Sales Organization. Depending on your reporting tool this can be more or less difficult. For example if you write your query manually you need just to put the right column in your select.
Another possibility would be to have a product/sales_org table, a table which combine the Product and the Sales_Org one:
Product_Sales_Org_id
Product_id
Sales_Org_id
Product_SO_number
...
This table will be child of the two dimension table and on the fact table you will have Product_Sales_Org_id column. Depending on Product and Sales Organization the Product_SO_number will return the correct number per SO.
If you want to have this in a star schema structure you can put Product/Sales_Org/Product_Sales_Org together in only one table like:
Product_Sales_Org_id
Product_id
Sales_Org_id
Product_desc
Sales_Org_desc
Product_SO_number
...
Sincerely I would go for the second solution, keep the Product and the Sales_Org tables separated, because they are two different business entities and implement the relationship table in the middle.
I hope this helps.
I have a problem, I am designing a database which will store different products and each product may have different details.
As an example it will need to store books with multiple authors and store software with different types of descriptions.
This is my current design:
Product_table
|ID|TYPE|COMPANY|
|1|1|1|
attr_table
|ID|NAME|
|1|ISBN10|
|2|ISBN13|
|3|Title|
|4|Author|
details_table
|ID|attr_id|value
|1|3|Book of adventures|
Connector_table
|id|pro_id|detail_id|
|1|1|1|
So the product table would only store the main product id, the company it belongs to and the type of product it is.
Then I would have the attribute table which lists each attribute a product could have, this will make it easier to add new types of products.
The details table will the hold all the values such as different authors, titles isbn10s etc.
And then the connector table would connect the product table and the details table.
My main worry is that the details table will get very large and will be storing lots of different data types.
What i would like would be to split up all of the different types into tables such as ISBN table and author tables.
If this is the case how could i link these tables up to the attr_table
Any help would be greatly appreciated.
Don't bother. You do not say what database you are using, but any reasonable database will be able to handle the details table. Databases are designed to handle big tables efficiently.
If it is really big, you might want to consider partitioning the table by some sort of theme.
Otherwise, just be sure that you have an index on the id in the table and probably on the attr_id as well. The structure should work fine.
I'd like to hear opinions on if it is better to keep forum categories and subcategories in the same table or in two separate tables...
Let's say you have a table ForumCategories. By adding a colum ParentId referencing the PK Id in the same table you could easily keep both the main categories and subcategories in the same table.
Alternatively, you could create a separate table ForumSubCategories and make the Id on that table a FK referencing PK Id column of the ForumCategories table.
Both solutions would work but what are the pros and cons of each solution?
Obviously, this is a more generic question that can apply to many other scenarios I just couldn't come up with a better phrasing in a hurry...
I can't think of any benefits of using 2 tables. Using 2 tables is going to constrain you to a 2 level tree. If you look at things as objects, then subcategories really are just category object. So put them in the same table. The 1 table structure will be simpler to design around and develop queries for.
If you know for sure that your forums will have only 2 levels of categories, then having 2 tables is reasonable.
Though storing categories in one table with foreign key to itself, basically, allows you store a tree of categories with virutally unlimited levels.
If they are the same entity (Category), you can link to itself. The parent would have a null for the parent ID or it could be linked to itself. This limits you to only one level unless you have a second table to handle the many-to-many possible relationships.
They must have the same fields or you're going to have unecessary fields for one or the other type. A separate table is why you would do this because they're not the same.
This is typical for an employee table. The supervisor is another employee record.