In SQL and relational databases, for what practical purposes are database views commonly created and used by developers and administrators?

Introduction / Context:
This question explores the role of views in SQL and relational databases. Views are virtual tables defined by a query, and they are widely used to simplify access, improve security, and abstract complex logic. Understanding why and how views are used is a fundamental skill for database developers and administrators.

Given Data / Assumptions:

- The question asks about the purposes for which views are used.- The options mention hiding rows, hiding columns, simplifying complex queries, and other effects.- We must choose the option that best summarizes valid uses.

Concept / Approach:
A view is defined by a SELECT statement and does not store data physically, but presents result sets as if they were tables. Views can limit which rows and columns users can see, and they can encapsulate joins, aggregations, and filters so that client code remains clean. When multiple options each describe real capabilities of views, an "all of the above" option is likely to be correct, provided that each listed use is valid.

Step-by-Step Solution:
Step 1: Consider the ability to hide rows. A view can filter base table rows using a WHERE clause so that users see only permitted data.Step 2: Consider the ability to hide columns. A view can project only selected columns, effectively hiding sensitive fields such as salary or password hashes.Step 3: Consider simplifying complex queries. A view can capture a complicated join or aggregation, so that applications can select from the view as if it were a simple table.Step 4: Check whether any of these uses conflict with how views work. All three are consistent with standard database theory and practice.Step 5: Realize that option D, which combines these valid uses, is therefore the correct choice.Step 6: Option E suggests physical reordering on disk, which is not a property of a view, so it can be rejected.

Verification / Alternative check:
Database documentation for systems such as Oracle, SQL Server, PostgreSQL, and MySQL all describe views as stored queries that provide logical data independence and security abstraction. They explicitly mention that views can restrict access to rows and columns and hide complexity. There is no reference to views changing the physical storage order of data, which confirms that the first three uses are valid and that option D is the best summary.

Why Other Options Are Wrong:
Options A, B, and C each describe a single valid use of views but omit the others, so they are incomplete answers. Option E is incorrect because physical storage is managed by tables and indexes; views do not directly control how data is stored on disk. Therefore, only option D correctly groups the genuine capabilities of views.

Common Pitfalls:
Students sometimes believe that views store their own copy of data or that they can be used to tune physical performance independently of base tables. Another common error is to think of views only as a convenience for complex queries, forgetting their important role in access control. In practice, views are often used to create secure, simplified interfaces over sensitive or complex schemas.

Final Answer:
Database views are used to hide rows, hide columns, and encapsulate complex SQL statements, so all of the listed purposes are valid.