There are 3 types of comments. One is a SQL-style which starts with '--', the other is C++ style starts with '//'. Both regards the entire line starts with the comment symbols is a comment line. The C style starts with '/*' and ends with '*/'
The following are examples of comments.
How to use --
-- This is a SQL-style comment.
How to use //
// This is a C++ style comment.
How to use /* */
/* This is a C-style comment.*/
/* This is an example to use two lines
as comment by using the C-style. */