In what way are they wildly different? I spent 15 years working in Oracle and the last 2 years working in Postgres. They are slightly different (Postgres adheres to the standard much more closely than Oracle), but 95% of my knowledge of SQL transferred from one to the other.
A simple example would be "how to select groupwise maximum" where Postgres would respond well to a correlated subquery and Oracle would respond well to a window function and derived table. The engines and optimizations are different.
