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Build a database I: Design tables for a new Access database Start with a plan Before you start planning, remember a key fact: Databases organize your information.

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Presentation on theme: "Build a database I: Design tables for a new Access database Start with a plan Before you start planning, remember a key fact: Databases organize your information."— Presentation transcript:

1 Build a database I: Design tables for a new Access database Start with a plan Before you start planning, remember a key fact: Databases organize your information into separate tables, and each table contains unique data. The database then uses relationships to join the data in the tables in a meaningful way. That set of tables and relationships is called a relational structure, which the picture shows.

2 Build a database I: Design tables for a new Access database Decide on a purpose The first step in planning a new database is to write down its purpose. In this case, you need to enter and manage your companys asset data. But dont stop there. Ask yourself who will use the database and how theyll use it. For example, the technician who fixes a defective machine has different information needs than the accountant who tracks costs. Make sure your purpose statement addresses those different needs and uses.

3 Build a database I: Design tables for a new Access database List the data you want to store A good database design helps ensure your data is complete, and most importantly, that its accurate. To reach those goals, start by listing the data you want to capture. You can start with your existing data in this case, your spreadsheet. Or, if you use paper ledgers or forms, gather examples of those. And dont hesitate to ask your coworkers what they need.

4 Build a database I: Design tables for a new Access database List the data you want to store Another way to identify the information you need to store is to create a flowchart of the tasks associated with your data. And while youre at it, think about the reports or mailings you want to produce from the database. Looking at the data you need to enter and consume can help you decide which data to store.

5 Build a database I: Design tables for a new Access database Group your data by subject As you list the data you want to capture, youll see it naturally falls into one or more subject matter categories or groups. Asset data, such as models, purchase dates, and costs. Support data who you call for help or spare parts. This category will probably include company names, addresses, phone numbers, and contact names. For example, your information may group itself like this:

6 Build a database I: Design tables for a new Access database Group your data by subject As you list the data you want to capture, youll see it naturally falls into one or more subject matter categories or groups. Supplier data, which looks a lot like support data because it includes companies and contact names. For example, your information may group itself like this: Grouping is important because each category can correspond to a table, such as Assets, Support, Suppliers.

7 Build a database I: Design tables for a new Access database Group your data by subject Your groups may not result in a complete list of tables, but theyre a good starting point. Just make sure each group contains unique data just the asset information in one group, only the supplier data in another, and so on.

8 Build a database I: Design tables for a new Access database From groups, fields The next step in your design is to list the fields for each table. In an Access table, columns are called fields and individual records are called rows. You plan your fields by deciding the specific information each of your groups should capture.

9 Build a database I: Design tables for a new Access database From groups, fields For your asset database, youll probably want to list each item and information about each item, such as purchase dates and costs. As part of this, try to reduce each field to its smallest logical component. In a good design, a field represents a single piece of data, and the name of the field clearly identifies that data.

10 Build a database I: Design tables for a new Access database From groups, fields As you work, you may find yourself wanting to use data from one table in another. For example, the picture shows that the Assets group includes fields for suppliers and support. Thats natural youre seeing how you need to relate your tables, and well discuss those relationships in just a bit. For now, include all the fields you think each table should have.

11 Build a database I: Design tables for a new Access database From groups, fields As you work, you may find yourself wanting to use data from one table in another. Finally, in case youre wondering, you dont plan rows. Those come naturally as you enter data in your fields.

12 Build a database I: Design tables for a new Access database Plan your primary keys A final step in your plan is to add a primary key field to each of your tables. A primary key is a field, or a combination of fields, with a value that makes each row in a table unique. Primary keys are another way to avoid duplicating your data, because you can never duplicate a value in a primary key field.

13 Build a database I: Design tables for a new Access database Plan your primary keys Access provides several ways to create primary keys. You can use existing values such as part numbers, but only if each value will always be unique. Once you define a field as a primary key, Access never lets you enter duplicate values in that field. Also, your key values should never change, because if they do your tables may become out of synch.

14 Build a database I: Design tables for a new Access database Plan your primary keys Access provides several ways to create primary keys. If your existing data wont work as a primary key, you can use an AutoNumber field. Access simply increments the value in that field by one whenever you add a new record.

15 Build a database I: Design tables for a new Access database Plan your primary keys So how do you plan primary keys? Start by adding an ID field, such as Asset_ID, to each of your tables. Or, if you want to use multiple columns of data to create a composite key, make a note next to each column you want to use.

16 Build a database I: Design tables for a new Access database A quick look at relationships So, youve divided your data into tables and listed the fields and primary keys. How do you relate your data back together? You create relationships by using the primary key field from one table as a field in another table. The picture shows this. You can see how the primary keys in the Suppliers and Support tables have become fields in the Assets table. Those duplicate fields in the Assets table are called foreign keys.

17 Build a database I: Design tables for a new Access database A quick look at relationships At this point, you may be thinking, Hang on, Ive just duplicated some data! Dont worry, this kind of duplication is okay. Primary key values are small, and you cant extract meaningful information from your database unless you use them in relationships. So, as a final step in your design, indicate your foreign key fields.


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