Perl for System Administration

Appendix D. The Fifteen-Minute SQL Tutorial

Relational databases can be an excellent tool for system administration. A relational database is accessed and administered using Structured Query Language (SQL) statements. As a result, it is a good idea for system administrators to learn at least the basics of SQL. The goal of this appendix is not to make you a full-time database programmer or even a real database administrator; that takes years of work and considerable expertise. However, we can look at enough SQL so you can begin to fake it. You may not be able to speak the language, but you’ll at least get the gist if someone speaks it at you, and you’ll know enough to go deeper into the subject if you need to. In Chapter 7, we’ll use these basic building blocks extensively when we integrate SQL and Perl.

SQL is a command language for performing operations on databases and their component parts. Tables are the component parts you’ll deal with most often. Their column and row structure makes them look a great deal like spreadsheets, but the resemblance is only surface-level. Table elements are not used to represent relationships to other elements—that is, table elements don’t hold formulas, they just hold data. Most SQL statements are devoted to working with the data in these rows and columns, allowing the user to add, delete, select, sort, and relate it between tables.

Let’s go over some of the operators offered by SQL. If you want to experiment with the operators we’ll be discussing, ...