Database Tables

If you threw your family's financial records into a filing cabinet without organizing them, you would have a mess. That is why most people organize their filing cabinets by putting related records into file folders. Your insurance papers go in one folder; your banking records go in another.

Likewise, you cannot throw your data into a database without separating the data into related groups. These groups are calledtables; a table is analogous to a file folder in a filing cabinet. Figure 17.1 illustrates a set of tables that hold financial information inside a business's database.

Figure 17.1 A database will contain data separated into groups called tables.

A database might contain many tables, each being a further refinement of related data. Your financial database might contain tables for accounts payable, customer records, accounts receivable, vendor records, employee records, and payroll details (such as hours worked during a given time period). The separate tables help you eliminate redundant data; when you produce a payroll report, Access might retrieve some information from your employee table (such as name and pay rate) and some information from your time tables (such as hours worked).

Note

Access is a relational database as opposed to a flat-file database. That means Access uses data from multiple tables instead of requiring you to duplicate data in two or more places. Therefore, if you increase a customer's discount, you need to change the discount in only one customer table rather than in the customer table, the pricing table, and the sales table.

Access stores all tables for a single database in one file that ends with the .mdb extension. By storing the complete database in one file, Access makes it easier for you to copy and back up your database. You never have to specify the .mdb extension when you create a database.

Note

You can import data from an Access database table into a Word document or Excel worksheet. The interaction between Access and the other Office products makes creating and reporting data simple. Appendix A, "Sharing Information Between Office 2003 Programs," explains more about sharing data between the Office products.

Records and Fields

To keep track of table data, Access breaks down each table into records and fields. In some ways, a table's structure looks similar to an Excel worksheet because of the rows and columns in a worksheet. As Figure 17.2 shows, a table's records are the rows, and a table's fields are the columns. Figure 17.2 shows a checkbook-register table; you usually organize your checkbook register just as you would organize a computerized version of a checkbook, so you will have little problem mastering Access's concepts of records and fields.

Figure 17.2 Tables have records (rows) and fields (columns).

Your table fields contain different data types. As Figure 17.2 shows, one field might hold a text description, whereas another might hold a dollar amount. Every item within the same field must be the same data type, but a table might contain several fields that differ in type. When you design your database, you are responsible for indicating to Access which data type you want for each field in your database tables.

The types of data that you can store in an Access database table are

• Text— Text data consists of letters, numbers, and special characters. You only report text data; you cannot calculate with it. A balance-due field would never be a text data type, but addresses, names, and Social Security numbers are examples of text fields. Generally, you store short text items (names, addresses, cities, product names, and part codes) in text fields.

• Memo— The memo field can hold an extremely large amount of text, including paragraphs. Memo fields consume a lot of space, and not all tables require them. Memos are great for documenting table entries and adding textual data that is free-form. For example, an Evaluation field for an employee database would be a good Memo candidate because you could then make entries that describe the employee's performance.

• Number— A number field holds numbers. Use this field to calculate values.

• Date/Time— These fields hold date and time values (similar to the date and time format in Excel). Access enables you to enter data into date and time fields using many formats. Additionally, Access respects your Windows international settings, so you can enter a date in your country's format.

• Currency— This field holds dollar amounts. Access keeps the dollar amounts rounded to the correct decimal alignment needed to match your currency designation. Access recognizes your Windows international settings and uses international currency amounts when needed.

• AutoNumber— This field holds sequential numbers, a different number for each record in the table.

• Yes/No— These fields hold Yes and No (or True and False) two-pronged values to indicate the existence or absence of an item or to indicate the answer to an implied question. For example, some items in an inventory database might be tagged for a special discount whereas others are not tagged.

• OLE object— This is an embedded object, such as a graph you create in Excel. Your Access databases can hold any kind of OLE-compatible embedded object.

• Hyperlink— This is an Internet Web site address. Such a field can hold an Internet address for a file as well as a network or an intranet address within your system network. When the database user clicks the hyperlink, Access shows the hyperlink's Web page or network file.

Note

The Internet integration of the other Office products extends to Access. When you click a table's hyperlink to an Internet Web page address, Access sends you to the Web page, logging you on to your Internet provider if necessary.