Knowing why you should create multiple tables

The prospect of creating multiple tables always intimidates beginning database users. Most often, they want to create one huge table that contains all of the information they need—in this case, a Customer table with all the sales performed by the customer and all the items sold or bought for each customer.

So, they create a single table containing a lot of fields, including fields for customer information (contact), sales information (date of sale, salesperson, amount paid, discounts, and so on), and the product information (quantity sold, product description, individual prices, and so on) for each sale. Such a table quickly grows to an unmanageable number of fields and continues growing as new items are added.

As you can see, the table design begins to take on a life of its own. After you’ve created the single table, it becomes even more difficult to maintain. You begin to realize that you have to input the customer information for every sale a customer makes (repeating the information over and over). The same is true for the items purchased for each sale, which is multiple items for each sale (thus, duplicating information again).

This makes the system more inefficient and prone to data-entry mistakes. The information stored in the table becomes inefficiently maintained—many fields may not be appropriate for each record, and the table ends up with a lot of empty fields.

It’s important to create tables that hold the minimum of information while still making the system easy to use and flexible enough to grow. To accomplish this, you need to consider making more than one table, with each table containing records with fields that are related only to the focus of that table. Then, after you create the tables, you link them so that you’re able to glean useful information from them. Although this process sounds extremely complex, the actual implementation is relatively easy. Again, this process of creating multiple tables from a single table is known as normalization (or normalizing your tables).

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