A database is a collection of data. You store databases in a relational database management system (RDMS). The RDMS is the basis for modern database systems like MySQL, SQL Server, Oracle, PostgreSQL, and others. These will be covered in more detail later in this chapter.
Understanding databases
Tables
In an RDMS, objects called tables store data. Tables are a collection of related data stored in columns and rows. The following screenshot is a cross-section of a table that contains data about baseball players' appearances in all-star games:
A NULL value in a table is a value that appears to be blank. It doesn't represent a string of blank spaces, zero, or a zero-length character string: it's a missing or unknown...
