In Oracle SQL, what is the difference between the RENAME statement and a column or table alias used in a SELECT statement?

Introduction / Context:
This question focuses on a very common confusion in Oracle SQL and other relational databases, namely the difference between changing an object name permanently and simply using a temporary name in a query. Interviewers often ask about the difference between the RENAME statement and aliases to see whether a candidate understands the impact on the data dictionary versus the impact on a single SELECT statement.

Given Data / Assumptions:

- The environment is Oracle Database with SQL support.
- RENAME refers to the DDL statement that changes the name of an existing schema object, usually a table or view.
- Alias refers to the AS keyword or implicit aliasing used in a SELECT statement for tables or columns.

Concept / Approach:
The core idea is that RENAME is a Data Definition Language operation. It changes the name of a database object stored in the data dictionary and affects all future references to that object name. An alias, on the other hand, is a query level feature. It gives a temporary alternate name to a table or column only for the duration of that SQL statement. Aliases improve readability and are used for self joins and calculations, but they do not modify any metadata.

Step-by-Step Solution:
Step 1: Recall that the RENAME statement syntax is similar to RENAME old_name TO new_name, and it is executed once to change the object name. Step 2: Remember that after RENAME executes successfully, all future references must use the new object name in SQL statements, grants, and dependencies. Step 3: Recall that an alias can be written as SELECT column_name AS col_alias FROM table_name t, where col_alias and t are aliases. Step 4: Understand that aliases exist only during the execution of that SQL statement. They do not change the underlying object name in the data dictionary. Step 5: Compare each option and select the one that correctly states that RENAME is permanent and alias is temporary.

Verification / Alternative check:
A simple verification is to imagine running a SELECT statement that uses a column alias and then querying USER_TABLES or USER_VIEWS. You will not see any change to the object name there, which proves an alias is not permanent. In contrast, after running RENAME on a table, the old name disappears from the dictionary views and only the new name remains, confirming that RENAME has a lasting impact.

Why Other Options Are Wrong:
Option B is wrong because alias does not permanently change anything. Option C is incorrect because RENAME is generally used for tables or views, not limited only to columns, and alias can be used for both columns and tables. Option D incorrectly reverses the effects and suggests that alias changes the underlying object name, which is not true. Only option A matches Oracle behavior.

Common Pitfalls:
Learners sometimes treat aliases as if they create new objects, which can lead to confusion when trying to reference an alias outside the statement. Another common mistake is to think that RENAME is a cosmetic operation like changing a column header in a report, while in fact it is a structural change that may impact existing code and privileges. Always separate metadata changes from query level cosmetic changes in your mind.

Final Answer:
RENAME permanently changes the name of a table or view, whereas an alias is a temporary name used only inside a specific SQL statement.