I've used Oracle SQL in the past, and I have to say that there isn't much difference between the structure of Oracle SQL and MySQL SQL.
If you already have some knowledge of MySQL, then there shouldn't be much of a problem migrating to Oracle.
You do have greater flexibility with Oracle, though, especially with the ability to create references and relationships between tables, and able to create sub-queries, which can be a great help with larger, more complex queries.
All I can suggest is get used to writing SQL queries using the Oracle interface first before trying to write SQL queries embedded within PHP. Oracle can be quite strict, so you must first familiarise yourself with the error messages that will "definitely" appear.
Have a look on the web-sites for some Oracle SQL tutorials - there are plenty to choose from.