Take an introductory SQL course before you attempt to learn any specific database software. The time investment will help you build a proper foundation and get started on the correct foot in the world of databases. If one value attribute may be in two records, the shared attribute is a poor choice for a primary key. You should probably also avoid sensitive values that raise privacy concerns, such as Social Security numbers. When you see a NULL value, interpret it as “unknown.” For example, if a quantity is NULL, that doesn’t necessarily mean that it’s zero. Similarly, if a text field holds a NULL value, it doesn’t mean that there isn’t an appropriate value—it’s simply unknown. Consider a database containing information about children who attend a particular school. If the person entering the record doesn’t 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. 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, and there are several free online database creators to choose from.
