The raw materials for a PL/SQL program are its lexical elements: comments, identifiers, operators, and functions. We'll briefly examine these individual bits and pieces before seeing how they fit together into a functioning program.
There are two types of comments in PL/SQL: single-line and multiline comments. Single-line comments begin with two dash marks.
-- This is a comment
Multiline comments are identical to Java multiline comments. (They are called multiline comments because they can span multiple lines, but they can also be limited to a single-line.) They begin with a slash-asterisk (/*) and end with an asterisk-slash (*/):
/* This is a multiline comment. */
Comments can begin anywhere on a line, ...