2. Selecting Primary Keys is an Extremely Important Decision
The selection of a primary key is one of the most critical decisions you’ll make in the design of a new database. The most important constraint is that you must ensure that the selected key is unique. If it’s possible that two records (past, present, or future) may share the same value for an attribute, it’s a poor choice for a primary key. When evaluating this constraint, you should think creatively. You'll also need to avoid sensitive values, such as Social Security Numbers, as they raise privacy concerns.

3. NULL Is Not Zero or the Empty String
NULL is a very special value in the world of databases, but it's something that beginners often get confused about. When you see a NULL value, interpret it as "unknown". If a quantity is NULL, that doesn't necessarily mean that the quantity is zero. Similarly, if a text field holds a NULL value, that doesn't mean that there isn't an appropriate value, it's simply unknown. For example, consider a database containing information about children who attend a particular school. If the secretary entering the record does not know a student's age a NULL value is used to indicate the "unknown" placeholder. The student certainly has an age, it's just not present in the database.

4. Converting Spreadsheets to Databases Saves Time
If you already have tons of data stored in Excel (or other) spreadsheets, you can save yourself mountains of time by converting those spreadsheets into database tables.

5. All Database Platforms Are NOT Created Equal
There are many different databases out there and all offer a variety of different features at different price points. Some are full-featured enterprise databases designed to host huge data warehouses serving multinational enterprises. Others are desktop databases better suited to tracking inventory for a small store with one or two users. Your business requirements will dictate the appropriate database platform for your needs.

Database Tables

Just like Excel tables, database tables consist of columns and rows. Each column contains a different type of attribute and each row corresponds to a single record. For example, imagine that we were building a database table that contained names and telephone numbers. We’d probably set up columns named “FirstName”, “LastName” and “TelephoneNumber.” Then we’d simply start adding rows underneath those columns that contained the data we’re planning to store.

If we were building a table of contact information for our business that has 50 employees, we’d wind up with a table that contains 50 rows.

Databases and Spreadsheets

At this point, you’re probably asking yourself an obvious question – if a database is so much like a spreadsheet, why can’t I just use a spreadsheet? Databases are actually much more powerful than spreadsheets in the way you’re able to manipulate data. Here are just a few of the actions that you can perform on a database that would be difficult if not impossible to perform on a spreadsheet:

• Retrieve all records that match certain criteria
• Update records in bulk
• Cross-reference records in different tables
• Perform complex aggregate calculations

You can correlate information from multiple tables in a database by creating foreign key relationships between the tables.