# Oracle Core CS Questions with Answers

8 previously-asked core cs questions from Oracle's hiring process, each with the correct answer and a worked explanation. Written against the company's actual test pattern.

_Source: Astra (https://useastra.in). Updated 2026-09-05._

### 1. Which SQL operation combines rows from two tables based on a related column?

A. JOIN
B. UNION
C. GROUP BY
D. WHERE

**Answer:** JOIN

**Explanation:** A JOIN links rows across tables using a matching column.

### 2. Which SQL command removes a table along with its structure?

A. DELETE
B. TRUNCATE
C. DROP
D. REMOVE

**Answer:** DROP

**Explanation:** DROP deletes the entire table including its definition; DELETE and TRUNCATE only remove rows.

### 3. What does the SQL UNION operator do?

A. Combines result sets and removes duplicates
B. Joins tables on a key
C. Filters rows
D. Sorts results

**Answer:** Combines result sets and removes duplicates

**Explanation:** UNION stacks the results of two queries and removes duplicate rows; UNION ALL keeps duplicates.

### 4. Which normal form lies between 3NF and 4NF?

A. 2NF
B. BCNF
C. 5NF
D. 1NF

**Answer:** BCNF

**Explanation:** Boyce-Codd Normal Form (BCNF) is a stricter version of 3NF and comes before 4NF.

### 5. What is a database trigger?

A. Code that runs automatically on a data event
B. A primary key
C. A backup file
D. An index

**Answer:** Code that runs automatically on a data event

**Explanation:** A trigger is procedural code that executes automatically in response to events like INSERT, UPDATE, or DELETE.

### 6. Which function returns the current date and time in Oracle SQL?

A. SYSDATE
B. NOW
C. GETDATE
D. CURRENT

**Answer:** SYSDATE

**Explanation:** Oracle uses SYSDATE; NOW is MySQL and GETDATE is SQL Server.

### 7. What is a stored procedure?

A. A precompiled set of SQL statements
B. A single table
C. A backup file
D. An index type

**Answer:** A precompiled set of SQL statements

**Explanation:** A stored procedure is reusable, precompiled SQL logic stored in the database and invoked by name.

### 8. Which isolation level prevents phantom reads?

A. Serializable
B. Read uncommitted
C. Read committed
D. Repeatable read

**Answer:** Serializable

**Explanation:** The Serializable isolation level is the strictest and prevents phantom reads.

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