Oracle Interview Questions and Answers for 2025

SQL Functions are an extremely powerful SQL feature. SQL functions can accept parameters but must always return a value. 1 

SQL functions are classified into two types: 

1. Single-Row Functions: These functions work on a single row to return a single result. 

Single-Row Function Types: 

• Character 
• Number  
• Date 
• Conversion  
• General 

2. Multiple-Row Functions: These functions act on groups of rows to return a single result for each group of rows. 

Multiple-Row Function Types: 

• AVG  
• COUNT 
• MAX  
• MIN 
• SUM  
• STDDEV  

In Java, the Java virtual machine controls the thread's life cycle. The following are the java thread states: 

• New  
• Runnable 
• Running 
• Non-Runnable (Blocked) 
• Terminated  

NEW denotes a newly established thread that has not yet begun execution. RUNNABLE is either running or ready to be executed, but it is awaiting resource allocation. BLOCKED is awaiting a monitor lock in order to enter or re-enter a synchronized block/method. If the thread scheduler has picked it, it is in the operating state. When the run() method of a thread terminates, it is said to be terminated or dead. 

This is a frequently asked question in Oracle interview questions.

The javac command reads source files containing Java module, package, and type declarations and compiles them into class files that operate on the Java Virtual Machine. Annotations in Java source files and classes can also be processed by the javac command. 

In Java, a Wrapper class is a type of class that offers a method for converting primitive data types into objects and vice versa. When a wrapper class is constructed, a new field is generated in which the primitive data types are stored. 

• Using SQL*Plus as a command-line tool. You may directly perform SQL statements using this tool. 
• Using a graphical user interface (GUI) tool such as SQL Developer. Such tools allow you to run SQL commands directly. 
• Oracle Enterprise Manager is being used. This is an indirect method of running a SQL query. When you use Oracle Enterprise Manager, some activities are implicitly transformed to SQL queries, which are then run against the database. 
• Create your own software. This is not a traditional method of running your queries, although it is often used. SQL queries are executed by any online or Windows software that uses an Oracle database as its backend. These applications are developed in a programming language such as.NET or JAVA, and they link to the database via a driver. 

One of the most frequently posed Oracle basic interview questions, be ready for it.

To acquire information about the existing users in the password file, use the "v$pwfile users" view. Run the SQL query below: 

SELECT * FROM v$pwfile users in sql; 

For each user in the password file, the query above will return four columns. USERNAME, SYSDBA, SYSOPER, and SYSASM are the column names. 

• The USERNAME field displays the user's username from the password file. 
• The SYSDBA field indicates whether or not the user has SYSDBA rights. 
• The SYSOPER field indicates whether or not the user has SYSOPER rights. 
• The SYSASM field indicates whether or not the user has SYSASM rights. 

In the Oracle database, the basic unit of data storage is the table. Data is organized into rows and columns. 

To construct a new table, use the "CREATE TABLE" command. 

In Oracle, a nested table is a data type that has columns for storing multi-valued properties. An whole sub table can be stored in a nested table. 

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One or more tablespaces or logical storage units can be found in an Oracle database. These tablespaces hold all of the data in a database. Each tablespace is made up of one or more data files. The data files are physical entities that adhere to the operating system on which Oracle is installed.

The command "ANALYZE" lets the user to execute numerous operations on an index, table or cluster. It is beneficial to: 

• To detect the table's or cluster's migrated and chained rows. 
• To validate an object's structure. 
• To collect statistics about objects used by the user and put them in the data dictionary. 
• To remove statistics from the data dictionary that were utilized by an item. 

The merge statement enables for the subsequent combining of data from two tables. It chooses data from the source table and inserts/updates it in the target table based on the query condition. Merge is a helpful command in data warehouse systems.

You can learn more about DBA from our Oracle DBA interview questions and answers site.

Oracle is a corporation. Oracle is a database server that maintains data in a highly organized manner. It enables users to save and retrieve relevant data in a multi-user environment, allowing several users to access the same data at the same time. All of this is done while maintaining great performance. A database server also prevents unwanted access and provides effective failure recovery options. A standby database is a database replica that is formed by backing up a primary database.

A DBA can create new users, delete current users, and change any environment variables or rights granted to other users. 

• Control database storage 
• Manage users and security 
• Organize schema objects 
• Monitoring and management of database performance Backup and recovery 
• Job scheduling and automation 

It's no surprise that this one pops up often in Oracle interview questions software engineer.

Because the backup is taken while the database is alive and operating, it is also known as an online backup. And when the backup can only take place when the database is shut down, it is referred to as Cold Backup, which is also known as Offline Backup.

Passwords for database users are saved in the database's data dictionary. When a user tries to log into the database, his or her username and password are compared to the values in the database. If the username and password match, the user is granted database access. The data dictionary is kept in the database and may be accessed as long as the database is open. The dictionary also contains administrator passwords. 

The data dictionary would be inaccessible until the database was locked. Because one of the administrator's responsibilities is to restart a down database, they must be able to log in even if the database is locked. That's where the password file comes in. A password file is an operating system file that is kept on a separate disc from the database. It saves the login and password for users with SYSDBA or SYSOPER access. When the database is unavailable, administrators with particular privileges are authenticated using password files. 

Data files contain all of the tables. The data file contains all of the data. The database data is stored in the data files. The data of relational database structures, such as tables and indexes, is physically stored in database data files.

Normalization is the process of organizing data in a database. This entails creating tables and developing relationships between them in accordance with rules aimed to secure data while also making the database more adaptable by eliminating redundancy and conflicting dependencies.

The recovery catalog is a database architecture that holds the metadata for data restoration and recovery activities that RMAN administers. A recovery catalog stores the metadata utilized by RMAN throughout the reinstallation and healing processes. Even if the target control file and its backups are deleted, the RMAN information remains in the recovery catalogue.

The benefits of utilizing a view in a table are as follows: 

• It is a subset of the information in the table. 
• It saves complicated inquiries. 
• It may combine numerous tables into one. 
• It takes up very little space. 
• It provides data from various angles. 

A common question in Oracle interview questions advanced, don't miss this one.

Oracle provides numerous methods for shutting down the database. 

• Normal Mode: By default, the database is shut down in normal mode. It is appropriate when no other clause is present. Before shutting down the database, it waits for all presently associated users to disconnect, and no new connections are authorized until the statement is published. The command line is as follows: 

SHUTDOWN NORMAL 

• Transactional Mode: Transactional mode aids in the shutdown of the database while enabling ongoing transactions to be completed. No new connections are allowed during this procedure, and the database is shut down when all transactions have completed. To shut down the database, use this command line. 

SHUTDOWN TRANSACTIONAL 

• Immediate Mode: When you know a power loss is imminent, you can activate urgent mode. All sessions will be disconnected, all active transactions will be rolled back, the database does not wait for existing database users to quit before proceeding, and the database will be shut down. There will be no requirement for instance recovery on the next startup. 

To instantly shut down a database, use the command SHUTDOWN with the IMMEDIATE argument.  

SHUTDOWN IMMEDIATE 

• Abort Mode: If you want to shut down the database immediately without any active transactions, use this abort method. No new connections or transactions may be established after the statement has been issued. The Oracle database ends all current client SQL queries automatically and does not wait for existing database users to disconnect. Uncommitted transactions will not be rolled back. The database automatically disconnects all related users. 

Use the SHUTDOWN command with the ABORT clause: 

SHUTDOWN ABORT 

A query is added to any view to define particular table rows and columns. A virtual table is a form of view. There are two sorts of views available: read-only and read-write.