Oracle Interview Questions and Answers for experienced

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100 Oracle Interview Questions and Answers

  1. What is the difference between COMMIT and ROLLBACK?

    • Answer: COMMIT saves all the changes made in a transaction to the database permanently. ROLLBACK undoes all the changes made in a transaction, restoring the database to its state before the transaction began.

  2. Explain the concept of PL/SQL.

    • Answer: PL/SQL (Procedural Language/SQL) is an extension of SQL that adds procedural programming capabilities to the language. It allows developers to write stored procedures, functions, triggers, and packages, enhancing database functionality and performance.

  3. What are indexes in Oracle? Explain different types.

    • Answer: Indexes are data structures that improve the speed of data retrieval operations on a database table at the cost of additional writes and storage space to maintain the index data. Types include B-tree (most common, for equality and range searches), Bitmap (efficient for columns with low cardinality), and Function-Based (on expressions or functions).

  4. Describe the different types of joins in SQL.

    • Answer: INNER JOIN (returns rows only when there is a match in both tables), LEFT (OUTER) JOIN (returns all rows from the left table, and the matched rows from the right table), RIGHT (OUTER) JOIN (returns all rows from the right table, and the matched rows from the left table), and FULL (OUTER) JOIN (returns all rows from both tables).

  5. How do you handle exceptions in PL/SQL?

    • Answer: Using exception handlers within a block of PL/SQL code. The `EXCEPTION` section allows you to catch specific exceptions (e.g., `NO_DATA_FOUND`, `DUP_VAL_ON_INDEX`) or use a generic `OTHERS` handler to catch any unhandled exceptions. You can then handle the exception appropriately, such as logging an error or displaying a user-friendly message.

  6. What are stored procedures? What are their advantages?

    • Answer: Stored procedures are pre-compiled SQL code stored in the database. Advantages include improved performance (due to pre-compilation), enhanced security (restricting direct access to tables), code reusability, and easier maintenance.

  7. Explain the concept of database triggers.

    • Answer: Database triggers are stored procedures that automatically execute in response to certain events on a particular table or view in a database. These events can include INSERT, UPDATE, or DELETE operations.

  8. What are views in Oracle?

    • Answer: Views are virtual tables based on the result-set of an SQL statement. They provide a customized view of the data without physically storing the data.

  9. How do you optimize SQL queries for performance?

    • Answer: Techniques include using appropriate indexes, optimizing join conditions, avoiding functions in `WHERE` clauses, using `EXISTS` instead of `COUNT(*)` in subqueries, and writing efficient queries by avoiding `SELECT *`.

  10. Explain different types of Oracle sequences.

    • Answer: Oracle sequences are database objects that generate unique numeric values. They are commonly used to provide primary key values. There's no specific "type" beyond configuration options like `INCREMENT BY`, `MINVALUE`, `MAXVALUE`, `CYCLE`, and `CACHE`.

  11. Explain the concept of data warehousing.

    • Answer: A data warehouse is a central repository of integrated data from one or more disparate sources. It's designed for querying and analysis rather than transaction processing, and is typically used for business intelligence and reporting.

  12. What is the difference between a clustered and a non-clustered index?

    • Answer: This question is relevant for SQL Server, not strictly Oracle. Oracle uses B-tree indexes, which have a similar function to clustered indexes in that they speed up queries, but not the same physical arrangement of data.

  13. What are materialized views?

    • Answer: Materialized views are pre-computed views that store the results of a query. They can significantly improve query performance, especially for complex or frequently executed queries.

  14. Describe different ways to manage transactions in Oracle.

    • Answer: Using `COMMIT`, `ROLLBACK`, and `SAVEPOINT` to manage transactions. You can also control transaction isolation levels.

  15. What is data partitioning in Oracle? What are its benefits?

    • Answer: Data partitioning divides a large table into smaller, more manageable pieces. Benefits include improved query performance, faster DDL operations, and simplified data archiving.

  16. Explain the concept of RAC (Real Application Clusters).

    • Answer: RAC is a high-availability and scalability feature that allows multiple instances of an Oracle database to run concurrently on different servers, providing redundancy and increased performance.

  17. What are the different types of database links?

    • Answer: Public database links are accessible to all users, while private database links are accessible only to the owner. They allow you to access data from other Oracle databases.

  18. How do you perform backups and recovery in Oracle?

    • Answer: Oracle provides various backup methods, including full backups, incremental backups, and RMAN (Recovery Manager). Recovery involves restoring from backups using RMAN or other tools.

  19. What are the different roles and privileges in Oracle?

    • Answer: Oracle uses a role-based access control (RBAC) system. Roles group related privileges together, allowing administrators to easily manage user access to database objects.

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