Денормализованная история (журнал) таблицы с налогом - да или нет?
Denormalized history (ledger) table with tax - yes or no?
Posted on September 27, 2022
In the world of database design, the decision to denormalize tables is often a topic of debate. One such situation arises when considering whether to include tax information in the denormalized history (ledger) table. In this article, we will explore the implications of including tax data in the denormalized table by examining a simplified example involving a Taxes table and an OrdersHistory table with tax values.
The Denormalized History (Ledger) Table
Let's start by understanding the concept of a denormalized history (ledger) table. In a typical database design, normalized tables are used to eliminate data redundancy and ensure data consistency. However, in some cases, denormalization is preferred for performance optimization purposes.
A denormalized history (ledger) table combines data from multiple related tables into a single table. This consolidation simplifies queries and avoids the need for complex joins, improving query performance. However, the decision to denormalize comes with trade-offs that need to be carefully considered.
The Taxes Table
Now, let's consider the Taxes table in our example. This table stores tax-related information such as tax percentages and durations. It serves as a reference table for retrieving tax data when needed.
| Tax Percentage | Durations |
|---|---|
| 8% | 2021-01-01 to 2021-12-31 |
| 10% | 2022-01-01 to present |
The OrdersHistory Table
Now, let's delve into the OrdersHistory table. This table contains purchase details, including tax values. It serves as a historical record of customer orders. Each entry in this table includes the tax value applicable at the time of the purchase.
| Purchase Details | Tax Value |
|---|---|
| Product A - Qty: 2 | $8.00 |
| Product B - Qty: 1 | $5.00 |
Now, the question arises - should the OrdersHistory table include tax information or should it rely on the Taxes table for retrieving tax data?
On one hand, including tax values in the OrdersHistory table simplifies queries. When retrieving historical data, you can directly access the tax values without the need for joins. This reduces the complexity of your queries and can improve query performance.
On the other hand, denormalizing the tax data can lead to data redundancy. If tax information changes in the future, you would need to update every entry in the OrdersHistory table to reflect the new tax values. This duplication of data can increase the risk of inconsistencies.
In this example, if we imagine a tax rate change in 2023, we would need to update all the entries in the OrdersHistory table from 2023 and onwards. This can be time-consuming and error-prone, especially if the table contains a large number of records.
Conclusion
As an experienced SEO copywriter, I would recommend carefully considering the advantages and disadvantages before denormalizing tax data in the history (ledger) table. While denormalization can improve query performance, it increases the risk of data redundancy and inconsistencies.
If performance optimization is a crucial requirement in your project and tax rates rarely change, including the tax information in the denormalized table could be a feasible solution. However, if tax rates frequently change, it would be wise to rely on the Taxes table for retrieving tax data when needed, even if it adds some complexity to your queries.
Ultimately, the decision should be based on the specific requirements and constraints of your project. Weigh the pros and cons carefully, and choose the approach that best aligns with the goals of your system.
Remember, designing a database involves carefully balancing trade-offs to ensure efficient data storage and retrieval. Stay mindful of data consistency, performance optimization, and maintainability throughout the decision-making process.