Display the Mean and Variace of purchased items

Hi

i am trying to create a program using WML, WMLSCRIPT, AND JSP. The task is to create a website to be displayed in the WAP Browser. In the website for a company called 'BargainBook' that sells books and the ERD diagram for this is attached as picture (see attachement).

So now I have just finished creating a login and register page and nearly done on purchase page BUT what I want to do is to find out how to display the MEAN and VARIANCE of purchased books in a given period of time (let say 1 week for example) . Plus how can I extend my ER Diagram in order to add this because I think I may need a separate entity (or table) for this.

Any explanation will be very much appreciated. As I said I think need a new table for this BUT I do not know what kind of record should be stored on it that would help with the calculation. And also, I would like to know the suitable SQL queries to calculate the mean and variance for a given period of time.



thanks

Can you explain what you mean by "MEAN and VARIANCE" - I know what the terms mean, but what do you think they mean and how what the comparison is against?

You don't need additional tables, I wouldn't have thought, for this as SQL (whatever flavor you are using) should be able to generate this information, on the fly as such.

I really think you should buy a book, either SQL and check out w3schools for bsaic tutorials on wml and wmlscript. I doubt you are going to get anyone to code this for you, unless you post a request in the "help wanted" forums. Post relevant code in the relevant forums and someone will try to help.

i think i get it. i think i need to store the time in the "Order" entity.