Prentice Hall Oracle Plsql By Example 3Rd Edition [Electronic resources] نسخه متنی

Lab 3.1 PL/SQL Programming Fundamentals

In most languages, you have only two sets of characters: numbers and letters. Some languages, such as Hebrew or Tibetan, have specific characters for vowels that are not placed in line with consonants. Additionally, other languages, such as Japanese, have three character sets: one for words originally taken from the Chinese language, another set for native Japanese words, and then a third for other foreign words. In order to speak any foreign language, you have to begin by learning these character sets. Then you progress to learn how to make words from these character sets. Finally, you learn the parts of speech and you can begin talking. You can think of PL/SQL as being a more complex language because it has many character types and, additionally, many types of words or lexical units that are made from these character sets. Once you learn these, you can progress to learn the structure of the PL/SQL language.

Character Types

The PL/SQL engine accepts four types of characters: letters, digits, symbols (*, +, -, =, etc.), and white space. When elements from one or more of these character types are joined together, they will create a lexical unit (these lexical units can be a combination of character types). The lexical units are the words of the PL/SQL language. First you need to learn the PL/SQL vocabulary, and then you will move on to the syntax, or grammar. Soon you can start talking in PL/SQL.

Although PL/SQL can be considered a language, don't try talking to your fellow programmers in PL/SQL. For example, at a dinner table of programmers, if you say, "BEGIN, LOOP FOR PEAS IN PLATE EXECUTE EAT PEAS, END LOOP, EXCEPTION WHEN BROCCOLI FOUND EXECUTE SEND TO PRESIDENT BUSH, END EAT PEAS," you may not be considered human. This type of language is reserved for Terminators and the like.

Lexical Units

A language such as English contains different parts of speech. Each part of speech, such as a verb or noun, behaves in a different way and must be used according to specific rules. Likewise, a programming language has lexical units that are the building blocks of the language. PL/SQL lexical units fall within one of the following five groups:

See Appendix B, "PL/SQL Formatting Guide," for details on formatting.

In the following exercises, you will practice putting these units together.