Top 40 Oracle Database Administrator Interview Questions

Oracle databases continue to be essential components of many big businesses and vital systems. Therefore, to maintain, optimize, and safeguard these databases, skilled DBAs are required. Here are the top 40 Oracle Database Administrator Interview Questions and Answers that are helpful for freshers and experienced professionals to get hired easily. Explore what our Oracle DBA course syllabus has in store for you.

Interview Questions and Answers for Oracle DBA Freshers

Here are some important Oracle database admin interview questions and answers. They are frequently asked Oracle DBA administrator interview questions.

1. What is a database?

An organized collection of structured data, or information, usually kept electronically in a computer system, is called a database. Data may be efficiently stored, retrieved, modified, and deleted due to the database.

2. What is a relational database?

A relational database creates relationships between tables by grouping data into tables with rows (records) and columns (attributes). A relational database is Oracle.

3. What is SQL?

A computer language called SQL (Structured Query Language) was created specifically for relational database management and manipulation.

4. What are the different types of SQL statements?

The various types of SQL statements are:

• DML: Data Manipulation Language (SELECT, INSERT, UPDATE, DELETE)
• DDL: Data Definition Language (CREATE, ALTER, DROP, TRUNCATE)
• DCL: Data Control Language (GRANT, REVOKE)
• TCL: Transaction Control Language (COMMIT, ROLLBACK, SAVEPOINT). 

5. What is normalization?

The practice of structuring data to improve data integrity and minimize redundancy is called normalization. It entails breaking up bigger tables into smaller ones and use relationships to connect them. 

6. What are the different normal forms?

A collection of guidelines known as normal forms aids in the organization of relational databases. By eliminating unnecessary data, they enhance data integrity. In database management systems (DBMS), the several standard forms are:

• Zero Normal Form (0NF): Unnormalized data is in zero normal form (0NF).
• First Normal Form (1NF): Deduplicated data with important characteristics recognized.
• Second Normal Form (2NF): Information with complete functional dependencies on the essential characteristics.
• Third Normal Form (3NF): Information with transitive connections eliminated.
• Boyce-Codd Normal Form (BCNF): Data that has removed all functional dependencies on non-key attributes is known as Boyce-Codd Normal Form (BCNF).
• Fourth Normal Form (4NF): Information with multivalued dependencies eliminated.
• Fifth Normal Form (5NF): Information with connect dependencies eliminated.
• Sixth Normal Form (6NF): Information with related variables broken down into irreducible parts.

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7. What is a primary key?

A column, or group of columns, that uniquely identifies every table row is called a primary key. Each record in a database table is uniquely identified by its primary key. It’s a column, or group of columns, with values specific to each row.  

8. What is a foreign key?

A column or group of columns in one database that point to the main key in another is called a foreign key. It creates a connection between the two tables.

9. What is a unique key?

Like a primary key, a unique key is a column or group of columns that uniquely identifies every row in a database; however, a table may contain more than one unique key. A unique key may permit NULL values, in contrast to a main key.

10. What is an index?

A data structure that speeds up data retrieval is called an index. It resembles a book’s index. 

• In DBMSs, indexing is a method that optimizes a database query’s searching time by utilizing data structures. 
• It facilitates quicker data retrieval from the database and speedier query results. Indexing improves the performance of databases. 
• Additionally, it uses less main memory space.

11. What is an Oracle instance?

The System Global Area (SGA) and background processes make up an Oracle instance. It is the environment in which an Oracle database operates. It holds logon and session information, processes SQL statements, serves database users, and maintains database data. 

12. What is an Oracle database?

The real data is stored in a group of data files called an Oracle database. It has a connection to an instance. A database management system (DBMS) that arranges and stores data in tables and columns is called an Oracle database. Businesses use it to store and manage data, and it works with a variety of operating systems.  

13. What is the SGA?

The term “SGA” refers to the “System Global Area,” a shared memory area in an Oracle database instance that houses data and control information used by all background and server processes. 

This includes shared SQL areas, cached data blocks, and other important information that enables multiple users to access the data at once.  Among its components are the redo log buffer, shared pool, and database buffer cache. 

14. What are background processes?

For the Oracle instance, background processes carry out a number of functions, including memory management, disk writing, and connection handling.

15. What is a tablespace?

An Oracle database’s logical storage unit is called a tablespace. Data files are arranged using it. In a database, a tablespace is a storage unit that arranges data into logical groups. It is a method for managing and storing massive items, tables, and indexes in databases.  

16. What is a data file?

The real data for a tablespace is stored in a physical file on disk called a data file. A data file is a type of computer file that contains information for use by a system or software. Text, numbers, pictures, movies, and more can all be found in data files.

17. What is a schema?

A schema is a model or framework used to arrange and analyze data. It may allude to a data model in computing or a cognitive model in psychology. A group of database objects (tables, views, indexes, etc.) connected to a user is called a schema.

18. What is a user in Oracle?

A user is a person with authorized access to the Oracle database system. In Oracle, a “user” is a unique account that enables a person to connect to the database and interact with its data. 

This account functions as a login credential with specific privileges to access and manipulate database objects, and each user owns a unique schema within the database that contains their tables and other data structures.

19. What is a view?

A saved query is called a view. It offers a method for customizing how data from one or more tables is presented. It is a named SQL query that is kept in the database’s data dictionary. It is a virtual table that does not hold data and is based on one or more tables.

20. What is a sequence?

A database object that produces a series of numbers is called a sequence. It is frequently employed to produce primary key values. Primary and unique keys in tables frequently employ these numbers. Utilize the Object Browser and the CREATE SEQUENCE command.

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Interview Questions and Answers for Oracle DBA Experienced Applicants

Here are the popular oracle database admin interview questions for experienced. They are the latest oracle dba interview questions answers for everyone.

1. Write a query to select all employees from the ’employees’ table. 

To review every column in the employee table, the SQL query will be: 

SELECT * FROM employee

The asterisk (*) symbol in the SELECT command instructs the database to select every column from the designated table.

2. Write a query to select the employee name and salary from the ’employees’ table where the salary is greater than 10000. 

To select the employee name and salary from the “employees” table, use the following query:

SELECT employee_name, salary FROM employees WHERE salary > 10000;

3. Write a query to find the highest salary in the ’employees’ table.

The query to find the highest salary in the ‘employees’ table is:

SELECT MAX(salary) FROM employees;

4. Write a query to find the average salary in the ’employees’ table.

The query to find the average salary in the ’employees’ table is:

SELECT AVG(salary) FROM employees;

5. Write a query to group employees by department and find the number of employees in each department. 

The query to group employees by department and find the number of employees in each department. 

SELECT department_id, COUNT(*) FROM employees GROUP BY department_id;

6. Write a query to join two tables (e.g., ’employees’ and ‘departments’) based on a common column (e.g., ‘department_id’). 

The query to join two tables (e.g., ’employees’ and ‘departments’) based on a common column:

SELECT e.employee_name, d.department_name FROM employees e JOIN departments d ON e.department_id = d.department_id;

7. What distinguishes the HAVING clause from the WHERE clause?

HAVING filters groups after the GROUP BY clause, but WHERE filters rows before grouping.

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8. What are some common aggregate functions in SQL?

COUNT(), SUM(), AVG(), MIN(), and MAX() are common SQL aggregate functions that are used to calculate several rows of data and return a single value, such as the total count, sum, average, minimum, and maximum value within a given column, respectively.

Each function’s explanation:

• COUNT(): Determines how many rows there are in a group or table.
• SUM(): Determines the sum of all the values in a column of numbers.
• AVG(): Determines a numeric column’s average value.
• MIN(): The smallest value in a column is returned by the MIN() function.
• MAX(): The largest value in a column is returned by the MAX() function.

9. What is a subquery? 

A query nested inside another query expression is called a subquery. Another name for it is a nested query or an inner query. 

• Subqueries aid in separating a statement’s components.
• They offer a substitute for intricate unions and joins.
• They can be used to locate particular data, such as a table’s minimum or maximum value.
• They are useful for identifying intricate linkages and patterns in data.

10. What is the difference between UNION and UNION ALL? 

Whereas UNION ALL retains every record, even duplicates, UNION eliminates duplicate rows.

The UNION command connects two or more SELECT statements while removing duplicates from the final result set, whereas the UNION ALL statement does not remove duplicates from the result.

UNION ALL is used to concatenate all records, including duplicates from the SELECT operation. 

11. What are some common performance tuning techniques in Oracle?

Typical Oracle performance optimization methods include the following:

• Instance Tuning: To prevent bottlenecks, allocate memory, and ascertain I/O requirements, take into account the database design.
• Query Optimization: Utilize indexes to expedite data retrieval, decrease response times, and enhance query performance.
• Automatic Workload Repository (AWR): Utilize this monitoring tool to gather, handle, and save performance data.
• Effective SQL: Employ partition pruning, meaningful aliases, bind variables, and only choose the columns that are required.
• Optimize Database Design: Identify and address resource bottlenecks and database irregularities.
• Minimize CPU Overhead: Verify that every CPU is being used.
• Optimize Instance Memory: Make that the memory settings of the database are set up correctly.
• Performance Planning: Obtain user input, establish performance objectives, and examine the operating systems of all systems that are involved.
• Regular Database Maintenance: Plan routine maintenance activities, such clearing out superfluous data and improving tables. 

12. What is an execution plan in Oracle?

The processes that the Oracle database takes to retrieve data from tables in response to a SQL query are known as an Oracle execution plan. The database internally creates the execution plan.

It explains how data from tables will be accessed by the database. It prepares data for the user issuing the statement by retrieving rows of data from the database.

It’s crucial to remember that various execution strategies may have varying budgets and timelines. An execution plan outlines the steps Oracle will take to carry out a query. It assists in locating performance snags.

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13. How is an execution plan analyzed? 

It uses programs such as SQL Developer or EXPLAIN PLAN. A database management system’s visual execution plan tool is usually used to navigate and interpret the plan step-by-step. 

• The main focus is on identifying full table scans, unnecessary sorts, and inefficient joins in order to restructure the query to use indexes and minimize resource usage. 
• An execution plan is examined by looking at its detailed breakdown of operations, including the order of operations, access methods (like index usage), estimated costs, and cardinality (number of rows affected).  

14. What are some common causes of poor performance in Oracle? 

Here are common reasons for Oracle database performance issues. These issues can result in slow query execution and general system sluggishness.  

• Ineffective SQL queries (such as missing indexes or poorly designed joins). 
• Insufficient hardware resources (CPU.
• Memory and disk I/O). 
• Improper database configuration (SGA/PGA sizing). 
• Poorly optimized stored procedures. 
• Excessive locking contention. 
• Out-of-date statistics. 
• Network bottlenecks.

15. How may a SQL query’s performance be enhanced? 

By minimizing entire table searches, employing suitable indexes, and streamlining the query logic. Best practices for optimizing SQL queries: 

• Make efficient use of indexes.
• Retrieving only relevant columns is preferable to using SELECT *.
• Make JOIN procedures more efficient.
• Reduce the number of subqueries you use.
• Retrieving unneeded or redundant data should be avoided.
• Make use of saved routines.
• Think about sharding and partitioning.
• Database tables should be normalized.

16. What are some different types of backups in Oracle? 

There are five types of backups as follows:

Full backups: A copy of a database’s whole contents is called a full backup. 

Incremental backups: Blocks that have changed since the last incremental backup are replicated in an incremental backup. Every block that has changed since the last complete backup is replicated in a cumulative incremental backup. 

Hot backups: Hot backups, also known as online backups, are carried out while the database is accessible and operational. During a hot backup, the database is still accessible for reading and updating. 

Cold backups: Cold backups, also known as offline backups, are carried out when the database is not accessible to users. All data, log, and control files need to be copied, and the database instance needs to be terminated. 

Recovery Manager (RMAN): Oracle comes with a built-in utility called Recovery Manager (RMAN) that can backup, restore, and recover database files. RMAN has the ability to automatically apply redo logs and incremental backups to restore a database to a certain point in time. 

17. What distinguishes a cold backup from a hot backup? 

When the database is online, a hot backup is made; when it is offline, a cold backup is made.

The key distinction is whether the system is online or offline during the backup process; 

• A “hot backup” is taken while the system is still operational and accessible to users, whereas a “cold backup” is taken when the system is fully shut down and unavailable to users. 
• While hot backups allow for nearly continuous operation with little interruption, they may take longer to finish because of continuous data changes.

18. What are redo logs used for? 

Redo logs document every modification made to the database. In the event of a failure, they are employed for recovery. 

• A key component of database recovery mechanisms, redo logs are used by databases to document all data changes. 
• This allows the system to recover and reapply those changes in the event of a system crash, effectively “redoing” any incomplete transactions and guaranteeing data integrity during recovery operations.  

Important details with redo logs:

• Data Capture: Each time a database is updated, inserted, or deleted, a “redo record” that details the modifications done to the data is recorded in the redo log.
• Crash Recovery: In the event of a system failure, the database can replay the changes that were made and return to its pre-crash state using the redo logs.
• Circular Buffer: Older entries are replaced when the log fills up in a circular buffer, which is how redo logs are usually designed.
• Archiving: For long-term backup and disaster recovery purposes, redo logs are often stored in a different location in database systems.

19. What do archive logs serve as? 

Redo logs are duplicates of archive logs. For point-in-time recovery, they are employed. Rollforward recovery and more sophisticated backup and recovery techniques require archive logs. They are made by mirroring the log path to a different location or copying log files from the existing log path.

The uses of archive logs:

• Backup and recovery: More sophisticated backup and recovery techniques make use of archive logs.
• Rollforward recovery: Rollforward recovery makes use of archive logs.
• Maintaining recovery points: Archival backups are used to keep a fixed recovery point on tape or the cloud.

20. How is recovery carried out in Oracle? 

Use programs such as Recovery Manager (RMAN). Recovery entails applying redo or archive logs and restoring backups.

• The Recovery Manager (RMAN) tool is the main tool used in Oracle for recovery. 
• It enables the backup and restoration of a whole database or individual data files by applying redo logs from the archive log to restore the database to a desired point in time. 
• Usually, a combination of full backups and incremental backups is used to effectively recover from data loss or system failures. 
• This procedure makes use of the idea of redo logs to track database changes, allowing recovery to a specific point in time.  

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Conclusion

In today’s data-driven environment, an Oracle DBA’s function is still vital. The fundamental duties of maintaining, optimizing, and safeguarding vital data remain crucial, even though the particular skills needed may change as a result of new technologies like automation and cloud computing. Enhance your database skills with our latest Oracle DBA interview questions answers. Thrive in your DBA career with our Oracle DBA course in Chennai.