PDO has the following advantages over the mysql_* functions:
- It’s cross database, meaning it’s the same interface for different relational databases.
- It helps protect against SQL injections.
- It’s much cleaner (uses an object-oriented approach).
This question has been asked before, you may want to take a look at the answers:
- Moving from mysql to mysqli or pdo?
- mysqli or PDO – what are the pros and cons?
If you are starting a new project, I would strictly suggest using PDO or a higher-level library/ORM. If you already have a lot of code written without it, it may not be worth it.