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How many Tables are needed

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  • How many Tables are needed

    I am getting confused trying to create tables for a database tracking :

    1) vendors

    3) Products

    4) product specifications

    There are multiple vendors , no one vendor makes all of the products. My fear is having too many tables or putting too much information in a table.

    so far I have:

    1) tblProdCategory ( product category)
    2) thlProdUPC ( Product UPC, ProdName, Prodsize, Description)
    3) tblProdSpec ( ProdUPC, ShelfLife, SellUnit, casesPerPallet, KgPer Case)
    4) tblVendors ( VendorName, VendorAddress, VendorCity, Vendor Postal)

    Not sure where to d\show products supplied by a given vendor

  • #2
    Re: How many Tables are needed

    Originally posted by clemkonan View Post
    Not sure where to d\show products supplied by a given vendor
    tblVendors [1:M] thlProdUPC - assuming that products are unique to vendor.

    If not:

    tblVendors [1:M] LinkingTable(vendor_id, product_id) [1:1] thlProdUPC
    Peter
    AlphaBase Solutions, LLC

    Peter@AlphaBaseSolutions.com
    https://www.alphabasesolutions.com


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    • #3
      Re: How many Tables are needed

      I would take a step back (or half a step). Before continuing with your table design get a better understanding of your data. Put the various bits of data into boxes or entities. Ask your self all kinds of questions about these entities and write them down, including the answers. You will end up going through this process a number of times revising your questions and answers as you go. Often answers to one question will lead to more questions. When you think you have your answers then the tables and their structures will be more clear.

      For example one of your entities is Vendor. What do they do(specifically in relation to the data you want to track).
      An answer may be something like: A vendor supplies a product to my company. Another question: How many products can a vendor supply; one, many? Is it possible to have a vendor in the database that has not yet supplied any products?

      The answers to these questions have obviously given rise to another entity called product. And also the relationship between Vendor and Product. Another question on the this relationship is; can a product be supplied by more than one vendor.

      If it turns out that a vendor can supply many products and a product can be supplied by many vendors you have a many to many relationship. Here is where your table design will start to look different from your entities. Alpha, along with most if not all database products, can not represent such a relationship directly so a join table is employed. This join table would be the link between Vendor and Product and would at the very least contain the primary key from each table.

      Looking at some of the fields you suggest for the products, specifically the specification data. I would be asking what this data is really referring to and what is it dependent on. Are there going to be multiple specifications for each product? Like, is there a possibility that a product will have more than one shelf life. Is it dependent on the product? If so then it probably only has one value and could go directly in the product table. CasesperPallet and KgperCase can often be dependent on the Vendor's shipping and production systems making these values dependent on both the Product and Vendor so these values might need to go in the Vendor/Product join table.

      Without knowing more specifically the business rules of your data it is difficult to suggest specific table structures. But then once you start asking these kinds of questions of your data I am sure it will start to become more clear to you as well.

      Hopefully I did not confuse the issue more.

      EDIT: I see Peter uses a few less words than I do. :)
      Last edited by Tim Kiebert; 02-12-2009, 12:52 AM.
      Tim Kiebert
      Eagle Creek Citrus
      A complex system that does not work is invariably found to have evolved from a simpler system that worked just fine.

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      • #4
        Re: How many Tables are needed

        Great advise I will go through the exercise. In short:

        1) A vendor can supply multiple products
        2) It would be advantageous to include a vendor ( prospective vendor) who is currently not shipping any products.
        3) A product as defined by its UPC number shares some unique features but if its the same product class ( oops got me!) the specification would be 99% identical for example 2% milk in 200ml, 500ml ,1 L is still 2% milk.
        4) The oops acknowledges your caution I was thinking product class = milk but I also have chocolate milk! a totally different animal different specification

        2 quick questions whats a joint table is this two separate tables forming a set? and when do I assign a primary key? I can save a table and Alpha five does not ask for one.

        Thanks

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        • #5
          Re: How many Tables are needed

          Originally posted by clemkonan View Post
          2 quick questions whats a joint table is this two separate tables forming a set? and when do I assign a primary key? I can save a table and Alpha five does not ask for one.
          You have to create the primary key yourself. My rule of thumb is to name it after the table - e.g. Vendor_Id, Product_Id, Spec_Id.

          Make sure to keep field & index names to 10-characters or less.

          Two or more joined tables is a "set" in Alpha.

          Note to Tim: In a previous life I was a loudmouth; I would never shut up. Now I try to practice KISS (Keep it Short & Simple).
          Peter
          AlphaBase Solutions, LLC

          Peter@AlphaBaseSolutions.com
          https://www.alphabasesolutions.com


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          • #6
            Re: How many Tables are needed

            :D
            KISS (Keep it Short & Simple).
            And here I had always thought this was universally an acronym for Keep it Simple Stupid!! Maybe it is and Peter is just euphemistically being nice? :p
            Mike
            __________________________________________
            It is only when we forget all our learning that we begin to know.
            It's not what you look at that matters, it's what you see.
            Henry David Thoreau
            __________________________________________



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            • #7
              Re: How many Tables are needed

              Originally posted by MikeC View Post
              And here I had always thought this was universally an acronym for Keep it Simple Stupid!! Maybe it is and Peter is just euphemistically being nice?
              Neither you nor Tim are stupid. But I used to be a motor mouth. These days my wife gets mad at me for not conversing.
              Peter
              AlphaBase Solutions, LLC

              Peter@AlphaBaseSolutions.com
              https://www.alphabasesolutions.com


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