Comparison of different SQL implementations: This is a phenomenal page listing how the different database server platforms handle standard SQL tasks, for instance row limited, ORDER BY, NATURAL JOINS, etc. Extremely well-researched.
The following tables compare how different DBMS products handle various SQL (and related) features. If possible, the tables also state how the implementations should do things, according to the SQL standard.
Just reading this will teach you something you didn’t know about your preferred platform.