The code in that example basically takes both of the supplied SQL statements, parses them (using the SQL::Parser module found in the SQL::Statement distro) and attempts (using Data::Dumper) to compare the AST (Abstract Syntax Tree) they created. The assumption is that even if the actual SQL strings are different (different case identifiers, different formatting or something) the AST created by a good SQL parser will be the same, meaning they are functionally identical.