Oracle developers are experts in designing and managing different areas of work in Oracle database software. This includes creating, modifying, and testing codes and scripts that allow a system to run multiple applications.
The workload of an Oracle developer may vary from company to company. As an Oracle developer, you might be responsible for things like system administration, web development, computer programming, network administration, design, database analysis, and web administration.
Getting hired as an Oracle software developer is no easy feat. With Oracle being one of the largest enterprise software companies in the world, competition for developer roles is fierce. If you have an Oracle interview coming up, proper preparation is key to standing out from the pack.
In this comprehensive guide, I’ll walk you through 15 of the most common Oracle software developer interview questions. Mastering these questions will get you ready to ace any Oracle coding, design or behavioral interview.
Let’s dive in!
1. Explain normalization in databases
Normalization is the process of organizing data in a database efficiently to minimize data redundancy and dependency. The advantages of normalization include:
-
Eliminating redundant data storage through breaking down large tables into smaller, related tables. This saves storage space.
-
Preventing data inconsistencies by eliminating duplicate data across tables.
-
Improving query performance through simplified queries focused on indexed columns.
-
Simplifying maintenance through isolated data sets. Changes need to be made in one place only.
-
Enforcing integrity constraints more easily with fewer columns to check.
Knowing database normalization principles shows you understand good database design and can implement it efficiently.
2. What is a database index and how does it improve performance?
A database index is a data structure that improves the speed of data retrieval from a database table. Indexes can be created on one or more columns of a table.
Indexes work by storing a small portion of the data from the table, but holding the location of the full data on disk. This makes lookups via the index faster than scanning the full table, especially for large tables.
Some ways indexes improve database performance:
-
Faster data search and retrieval
-
Faster sorting and grouping of data
-
More efficient joins between database tables
-
Improved overall speed for applications accessing indexed data
Understanding indexes is key for any developer working with Oracle databases.
3. Explain SQL and NoSQL databases and their key differences
SQL databases store data in tables with predefined schemas and use Structured Query Language (SQL) to interact with the data. Examples are Oracle, MySQL, and Microsoft SQL Server.
NoSQL databases have flexible schemas without fixed table structures and use various APIs to query and interact with the data. Examples are MongoDB, Cassandra, and HBase.
Key differences:
-
SQL databases are relational while NoSQL databases are non-relational.
-
SQL databases have fixed schemas while NoSQL databases have dynamic schemas.
-
SQL databases excel at complex queries while NoSQL databases are optimized for simple queries, availability, and scalability.
-
SQL databases follow ACID consistency while NoSQL databases follow CAP consistency.
Knowing when to use SQL vs NoSQL databases is an important skill for Oracle developers.
4. What are database transactions and what are their key properties?
A database transaction is a sequence of operations performed on a database as a single logical unit. Transactions have four key properties known as ACID:
-
Atomicity – Either all operations in a transaction succeed or the entire transaction is rolled back.
-
Consistency – A completed transaction takes the database from one valid state to another.
-
Isolation – Concurrent transactions execute independently without interference.
-
Durability – Once committed, a transaction persists even in the event of system failure.
Understanding transactions ensures developers implement robust, reliable systems resistant to faults and errors.
5. Explain database triggers and how they are used
Database triggers are procedures automatically executed in response to create, update, insert or delete events on a table. Triggers enhance database functionality and enable complex business logic in a database itself.
Common uses of database triggers include:
- Enforcing complex business rules and referential integrity
- Auditing data modifications
- Automatically derived column values
- Cascading changes to related tables
- Logging events transparently
- Gathering statistics on table access
Triggers are powerful tools for Oracle developers. Knowing triggers expands your ability to implement logic within the Oracle database.
6. How would you improve performance of a slow database query?
Some ways to improve performance of a slow database query include:
-
Add suitable indexes on columns used in the query to enable indexed lookups.
-
Tune the database and operating system configuration like memory, cpu and IO settings.
-
Refactor complex joins into simpler joins that are faster to execute.
-
Avoid expensive operators like ORDER BY and DISTINCT unless required.
-
Minimize full table scans by filtering on indexed columns.
-
Denormalize data into fewer tables to reduce join complexity.
-
Check for missing indexes and create if needed.
-
Review the query execution plan and optimize complex steps.
-
Tune SQL statements to avoid overfetching and restrict rows and columns selected.
Diagnosing and optimizing slow queries requires deep knowledge of Oracle database performance.
7. Explain database normalization forms (1NF, 2NF, 3NF, BCNF)
First normal form (1NF) – Eliminate repeating groups in tables. Ensure atomic values by separating columns with multiple values into separate tables.
Second normal form (2NF) – Eliminate redundant data by separating tables further to ensure no non-prime attribute depends on a part of a candidate key.
Third normal form (3NF) – Eliminate columns not dependent on the primary key by separating tables further. Ensures no non-prime attribute depends on non-key attributes.
Boyce–Codd normal form (BCNF) – Stricter version of 3NF where no non-trivial functional dependencies exist between candidate keys and non-prime attributes.
Normalization forms build on each other progressively to eliminate data redundancy and dependency issues. Higher normal forms lead to better database design.
8. How would you handle database concurrency issues?
Some ways to handle database concurrency issues from simultaneous transactions include:
-
Using transaction isolation levels like READ COMMITTED to isolate transactions.
-
Implementing proper database locking to prevent dirty reads.
-
Making transactions short and fast to minimize locking.
-
Using a queue with FIFO ordering to sequence transactions.
-
Designing idempotent transactions that can be safely rerun.
-
Handling DeadlockException and retry deadlocked transactions.
-
Using SELECT FOR UPDATE to lock queried rows from changes.
-
Building applications to handle transaction retries from concurrency failures.
Concurrency issues will arise in any multi-user database. As an Oracle developer, you must know how to mitigate these issues.
9. How would you optimize a slow-running SQL query?
Some techniques to optimize slow SQL queries are:
-
Add indexes on filtered columns to reduce full table scans.
-
Rewrite complex JOINs into faster simpler JOINs when possible.
-
Avoid SELECT * and select only required columns.
-
Use EXISTS instead of IN for subqueries with large tables.
-
Tune and optimize poorly performing subqueries.
-
Increase cache sizes for frequently accessed objects.
-
Collect statistics on objects using stale or missing statistics.
-
Review the query execution plan to identify bottlenecks.
-
Use tools like EXPLAIN PLAN to get insights into SQL performance.
-
Refactor queries to reduce I/O wait times when possible.
SQL optimization is an essential skill for any Oracle developer.
10. What are the differences between clustered and non-clustered indexes?
Clustered indexes physically sort table data in order based on the index key. Only one clustered index can exist per table.
Non-clustered indexes contain the index key along with row locators pointing to the actual data on disk. Multiple non-clustered indexes can exist per table.
Key differences:
-
Clustered indexes reorder table data while non-clustered indexes only contain row pointers.
-
Clustered indexes eliminate bookmark lookups but are slower for some operations.
-
A clustered index can greatly improve range queries but slow down OLTP performance.
-
Non-clustered indexes require key lookups to fetch actual data pages.
-
Tables can have only one clustered index but many non-clustered indexes.
Understanding index types allows proper use for optimized performance.
11. You are tasked with troubleshooting a slow Oracle database. Where would you start?
Some good places to start troubleshooting performance issues with an Oracle database are:
-
Review slow SQL queries using the AWR report to identify top CPU or I/O intensive ones. Focus optimization efforts on these.
-
Check database wait events through AWR to identify top wait classes like CPU, User I/O, etc. Address wait event causes.
-
Review AWR statistics for high load SQL and identify trends like poor index usage, high buffer gets, etc.
Salaries for Oracle developers range between $72K and $112K with the median being $94K.
- Degrees (associates or equivalent technical training, bachelors, masters)
- Years of Experience
- Location
- How you are reported to (how senior the manager you work for is and how many direct reports you have)
- Level of Performance – exceeding expectations
Be ready for anything with the interview simulator.
Oracle Developer Interview Questions
Question: Can you provide an overview of Oracle?
The interviewer will ask this usual opening or general question to start the conversation, find out more about your background, and get some information they can use for other questions they will ask.
Example: “Oracle is one of the more popular databases and was developed by the Oracle Corporation. It is the foundation for other applications developed by both Oracle and third parties. Since it uses relational management concepts, it is referred to as a relational database management system or RDBMS. Some of its applications include online transaction processing, data warehousing, and enterprise computing. ”.
Question: What is the nomenclature used to identify Oracle database software releases?
Explanation: This is a technical question. As an Oracle developer, you can expect that technical and operational questions will make up most of the interview. These are best responded to briefly and directly with little embellishment. The interviewer will ask a follow-up question if they need additional information.
Example: “Oracle has a specific nomenclature which they use for each release of the Oracle database software. This helps developers as well as users identify which version of the software they are working with. A typical format is release 10. 1. 0. 1. 1. Each of these numbers has a specific meaning which are:
- 10: major DB release number
- 1: DB maintenance release number
- 0: application server release number
- 1: component-specific release number
- 1: platform-specific release number”
Question: What process is used to create privileges in Oracle?
Explanation: This is an operational question. Much like technical questions, operational questions explore your knowledge and skills within the Oracle developer profession. Operational questions seek to understand how you go about doing your job.
For instance, “Privileges in Oracle” mean the ability to run queries and get to other database objects. The two classes of privileges include user system privilege. The system privilege provides greater access to the database and the ability to do more. Privileges are assigned using the following command string:
[sql]GRANT user1 TO user2 WITH MANAGER OPTION;[/sql]”
Question: Could you explain what the term “VArray” means in Oracle and how it is used?
This is a technical question that asks you to define a word and then talk about how it is used in the job you are interviewing for. This is the typical structure of a technical question. Remember to keep your answer short and to the point. The interviewer will ask a follow-up question if they need additional information.
Example: “VArray is a data type used by Oracle to enable columns to contain multivalued attributes. It can also hold a bounded array of values. ”.
Question: What command is used to obtain the details of the fields in a table?
Explanation: This question asks for a specific command to accomplish the task defined in the question. You answer this question by stating that command and then describing what it does.
Example: “The command used to get the details of fields of a specified table is describe.”
Question: Can you discuss the differences between the rename and alias commands in Oracle?
Explanation: This question asks you to compare two similar but different commands within Oracle. What does each word mean and how are they different from each other is the best way to answer this question.
Example: “Both rename and alias are commands used to name a table or column within Oracle. What makes them different is that alias gives the table or column a different name while keeping the original one. rename gives these things a permanent name that replaces the current one. ”.
Question: How do you differentiate between VARCHAR and VARCHAR2?
Explanation: Here is another technical question asking you to define the differences between two similar terms. Again, begin your answer by explaining what the terms mean and how they work. Then, quickly go over the differences between them.
Example: “Both VARCHAR and VARCHAR2 are Oracle data types used to store character strings of variable length. One difference between them is VARCHAR2 can store twice the number of bytes as VARCHAR, 4000 vs. 2000. Also, VARCHAR will keep a space for characters defined during declaration even if they aren’t used, but VARCHAR2 will free up any space that isn’t being used. ”.
Question: What are the differences between Oracle’s TRUNCATE and DELETE commands?
Explanation: This is another technical question asking you to distinguish between two different commands within Oracle. As the interview progresses, the questions will become more specific and more difficult. This indicates the interviewer is gaining confidence in your abilities and is willing to explore more complex topics. Continue to answer these questions just as you did the easier ones.
Example: “Both the TRUNCATE and DELETE are commands used to delete data from the database. The differences between these two similar commands are:
It is not possible to undo the TRUNCATE command, but it is possible to undo the DELETE command.
DELETE is a DML operation, and TRUNCATE is a DDL operation.
TRUNCATE frees the object’s storage space, but DELETE does not.”
Question: Can you describe what a RAW datatype is and how it is used?
This is a typical technical question where you have to first explain what a word means and then explain how it is used. As mentioned before, technical questions should be answered briefly and directly. You should anticipate a follow-up question any time you respond to a technical question. This will indicate the interviewer either needs more information or has a specific interest in this topic.
Example: “A RAW datatype is used to store variable-length binary data or byte strings. SQL doesn’t know how to convert this type of data, so when RAW data is sent to another system, it can’t be used. Also, RAW data types can only be queried or inserted in a table. ”.
What does the word “joins” mean in Oracle? Could you name a few different kinds of joins?
Explanation: The interviewer is continuing to ask you technical questions. As an Oracle developer, the best way to get ready for an interview is to first read the job posting and make a list of the requirements for the job. You should then research the company, its products, and the software it develops. This will give you an idea of the type of methodologies, commands, processes, and procedures they use. Once you know these, refresh yourself on typical Oracle terms, development methodologies, and commands.
Example: “Within Oracle, joins are used to extract data from multiple tables using common columns or conditions. The different types of joins include inner, outer, cross, equi, anti, and semi. ”.
Top 50 Oracle Interview Questions and Answers | Questions for Freshers and Experienced | Edureka
FAQ
How to prepare for an interview at Oracle?
Are Oracle interviews hard?
What does a software developer do at Oracle?
Is it easy to crack an Oracle interview?
