1. SQL Forms the Core of Relational Databases
You can't avoid it. The Structured Query Language forms the core of all relational databases. It provides a uniform interface to Oracle, SQL Server, Access and other relational databases and is a "must learn" for all aspiring database users. In fact, I encourage you to take an introductory SQL course before you even attempt to learn any specific database software. The investment of time will help you build a proper foundation and get started in the world of databases on the correct foot.

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.