In SQL, what can views be used to hide from end users when designing secure and maintainable database applications?

Introduction / Context:
Views are a core feature of SQL databases and play an important role in abstraction and security. They allow database designers to present a simplified and restricted view of data to application users. This question asks what exactly views can hide, which is fundamental for understanding how views support both usability and security in a database system.

Given Data / Assumptions:

• We are considering standard SQL views created with a CREATE VIEW statement.
• Views are virtual tables based on underlying base tables.
• We are interested in what aspects of the underlying data or queries can be hidden from the user.
• User access to the view may be granted without giving direct access to the base tables.

Concept / Approach:
A view is essentially a saved query that behaves like a virtual table. Because applications query the view instead of the base tables, the view can hide complexity and restrict access. It can encapsulate long and complex joins, filter out rows that users should not see, and expose only certain columns. The correct option will mention all these uses together and clearly distinguish views from low level server or hardware features that they do not hide.

Step-by-Step Solution:
1. Recall that the definition of a view is a SELECT statement stored as a virtual table.2. When a user queries a view, they do not see the underlying SELECT statement unless they have permission to inspect metadata. This hides complicated SQL syntax.3. The view can include a WHERE clause so that only certain rows are visible.4. The SELECT list can include only the columns that should be exposed, hiding sensitive columns.5. Option A states that views can hide complicated SQL syntax, rows, and columns. This matches the behaviour described above.6. Option B refers only to physical storage devices, which are not the focus of views.7. Option C limits views to hiding primary keys only, which is far too narrow.8. Option D mentions network ports, which are part of server configuration, not view functionality.9. Therefore, Option A is correct.

Verification / Alternative check:
You can verify this by creating a view such as SELECT name, city FROM customers WHERE status = active. Users who query this view will only see active customers and only the name and city fields. They do not see inactive customers or other columns like credit limit or internal identifiers. They also do not need to know that the view joins multiple tables or applies complex conditions. This example confirms that views hide syntax, rows, and columns.

Why Other Options Are Wrong:
Option B is wrong because views have nothing to do with the underlying storage devices.Option C is wrong because views can hide any combination of columns, not only primary keys.Option D is wrong because network ports are controlled by the database server configuration and firewall, not by views.

Common Pitfalls:
Some learners think of views only as performance tools, assuming they always speed up queries. In reality, views are primarily an abstraction and security mechanism. Another mistake is believing that views physically store data; in most databases, they are logical and recompute results at query time, unless materialized views are used. Understanding what views can hide helps you design better security boundaries and clearer application level data models.

Final Answer:
Views can hide complicated SQL syntax, specific rows, and specific columns from users.