in SQL, can there be hidden/encrypted data?

Question

when selecting a table, can a user only see certain columns or rows, while a developer can access the rest of the table?

Answer 1

MySQL has built-in encryption, encoding, hashing and compression functions (these are separate and distinct).
Views are often used for custom output displays
Stored procedures can do scripty-like things
You can indeed just give permission to columns
Encrypted data is a requirement to meet credit card (etc) security standards.
Guideline packs are well-written and freely available.

Answer 2

Oracle SQL also allows for hidden columns, but not hidden data within a visible column. as for encrypted, I have not seen anything natively encrypted by Oracle except for the ora hash, but I don't think that fits what you're asking.