Learning Oracle PL/SQL [Paperback]

In this chapter:
What Is PL/SQL?
Why Use PL/SQL?
What You Need to Get Started with PL/SQL

Let's start at the beginning and take a look at what Procedural Language/Structured Query Language (PL/SQL) really is, what it is good for, and how it fits into the world.

What Is PL/SQL?
Pick up most any reference book about PL/SQL and you'll read that it is Oracle's "procedural extension to Structured Query Language (SQL)." If that definition doesn't help much, consider what it assumes you know:

· What a computer "language" is
· What "procedural" means in this context
· Some concept of Structured Query Language, including the notion that SQL is not procedural
· The idea of a language "extension"

Let's look at each concept in turn.

A computer language is a particular way of giving instructions to (that is, programming) a computer. Computer languages tend to have a small vocabulary compared to regular human language. In addition, the way you can use the language vocabulary--that is, the grammar--is much less flexible than human language. These limitations occur because computers take everything literally; they have no way of reading between the lines and assuming what you intended.

Procedural refers to a series of ordered steps that the computer should follow to produce a result. This type of language also includes data structures that hold information that can be used multiple times. The individual statements could be expressed as a flow chart (although flow charts are out of fashion these days). Programs written in such a language use its sequential, conditional, and iterative constructs to express algorithms. So this part of the PL/SQL's definition is just saying that it is in the same family of languages as BASIC, COBOL, FORTRAN, Pascal, and C. For a description of how procedural languages contrast with three other common language categories, see the following sidebar.

Structured Query Language is a language based on set theory, so it is all about manipulating sets of data. SQL consists of a relatively small number of main commands such as SELECT, INSERT, CREATE, and GRANT; in fact, each statement accomplishes what might take hundreds of lines of procedural code to accomplish. That's one reason SQL-based databases are so widely used. The big joke about the name "SQL" is that it is not really structured, is not just for queries, and (some argue) is not even a real language. Nevertheless, it's the closest thing there is to a lingua franca for relational databases such as Oracle's database server, IBM's DB2, and Microsoft's SQL Server.

A language extension is a set of features that somehow enhance an existing language. This phrase might imply, incorrectly, that PL/SQL is a special version of SQL. That isn't the case, however. PL/SQL is a programming language in its own right; it has its own syntax, its own rules, and its own compiler. You can write PL/SQL programs with or without any SQL statements. Some authors assert that PL/SQL is a superset of SQL, but that's a bit of an overstatement, because only the most common SQL statements can be used easily in a PL/SQL program.

PL/SQL, then, is a language that is closely related to SQL, but one that allows you to write programs as an ordered series of statements. Or, if you want a definition of PL/SQL that befits a programmer:

PL/SQL is a procedural (Algol-like) language with support for named program units and packages; much of its syntax is borrowed from Ada, and from Oracle's SQL it derives its datatype space and many built-in functions.

But if that doesn't make any sense, don't worry about it! You'll get the same message in plain English in the forthcoming pages.