Storing calculated values in a database can lead to conflicts when values are updated and the resulting calculation is not. The best approach to dealing with calculations is to not store the end result, but rather, calculate when needed.
- [Instructor] Another source of common data conflicts…occurs when stored values are simply calculated…from other information that we're already storing…or keeping track of.…The problem is that if one value changes,…then we need to be sure to update the calculation as well.…Here's an example.…Let's take a look again at the invoices…for our olive oil sales.…We can see that Delish Food purchased…two bottles of our First Cold Press oil.…If we look up the price in the products table,…we can see that the First Cold Press olive oil…is $10 per bottle.…So the invoice correctly shows the total due as $20.…
This is good and accurate information for now,…but what happens if something changes?…If the order quantity gets changed, from say two to four,…then we also need to have the database management system…update the total price as well,…to reflect the new total due as $40 instead of 20.…Or, if the price per bottle change…in the products table to $15, then again,…the total price in the invoices table…would need to be updated.…
Adam Wilbert covers the basics of relational database design, regardless of whether you use Access, FileMaker, Open Office, or SQL Server. Learn how to prevent data anomalies, gather requirements to plan your design, and develop a conceptual data model—translating your ideas into components like tables, relationships, queries, and views. Plus, learn about logical design considerations that can help you construct a database that is easy to maintain.
- Identify the three rules of relations.
- Summarize the four stages of developing a relational database.
- Describe a strategy one might use to ensure a database remains flexible in terms of the questions a user can ask.
- Explain how to avoid scope creep.
- Recall the characteristics of a Lookup Table.
- Recognize situations in which denormalization would be beneficial.
- Understand the types of relationships modeled by junction tables.
- Define referential integrity.
Skill Level Beginner
1. Relational Database Basics
Relational structures3m 46s
2. Preventing Data Anomalies
3. Gathering Requirements
4. Developing the Conceptual Data Model
5. Normalizing Your Data
6. Logical Design Considerations
7. Developing the Physical Database
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