It’s a great time to become a database developer, and Oracle Developer skills are a must to break into the field. One of the most trusted and popular relational databases, Oracle is widely used across all industries, and Oracle DBAs are high in demand. Some of the top Oracle job roles are Oracle developers, Oracle DBA, Oracle technical consultant, application developer, principal consultant, etc.
Whether you are a fresher looking to gain an entry into the web development industry or an experienced professional wanting to advance your career, you need to brush up your knowledge before an Oracle interview. If that sounds like you, read on. In this blog, we cover the most common Oracle interview questions and answers to crack your next interview.
We have arranged the questions and answers in three categories: Basic, intermediate, and advanced Oracle interview questions.
Basic Oracle Interview Questions
1. What are schema objects?
Schema objects are tables, indexes, databases, views, sequences, synonyms, triggers, functions, procedures, and packages.
2. What are the components of physical database structure in the Oracle database?
The components of the physical database structure are:
One or more Data Files
Two or more Redo Log Files
One or more Control Files
3. What are the components of logical database structure in Oracle database?
The components of the physical database structure are:
Tablespaces – set of related logical structures or Logical Storage Unit
Database Schema Objects – a collection of database objects owned by a specific user
4. Differentiate between Varchar and varchar2.
Varchar and Varchar2 are data types in Oracle to store character strings of varying lengths. While Varchar can store characters up to 2000 bytes, Varchar2 can store up to 4000 bytes. Varchar will hold space for all characters defined during declaration. Varchar2 will free up the space for characters that were unused.
5. What is an Oracle table?
A table is the basic unit of data storage in the Oracle database. Data is stored in rows and columns.
“CREATE TABLE” statement is used to create a new table.
6. What is a nested table?
Nested table is a data type in Oracle used to hold columns for storing multi-valued attributes. A nested table can hold an entire sub table.
7. How are comments represented in Oracle?
We can represent comments in Oracle in the following two ways:
Two dashes (–) before the line starts – Single statement
For block of statement, we can use /*—— */ to represent it as comments
8. What is the relationship between database, tablespace and data file?
An Oracle database can contain one or more tablespaces or logical storage units. These tablespaces collectively store all the data in a database. Each tablespace consists of one or more files called data files. The data files are physical structures conforming to the operating system in which Oracle is running.
9. What are database objects in Oracle?
Various Oracle database objects are:
Tables – set of elements arranged in vertical and horizontal manner
Tablespaces – logical storage unit
Views – Virtual table derived from one or more tables.
Indexes – performance tuning method for record processing.
Synonyms – name for tables
10. Explain the ANALYZE command in Oracle.
The “ANALYZE” command allows the user to perform various functions on index, table or cluster. It helps:
To identify migrated and chained rows of the table or cluster.
To validate structure of an object
To collect statistics about objects used by user, which are then stored onto the data dictionary
To delete statistics used by an object from the data dictionary
11. What types of Joins are used in SUBQUERIES?
A join is used to compare and combine specific rows of data from two or more tables in a database. The various joins are:
Self Join – to join table with itself
Outer Join – to join matching data and some dissimilar data from more than one table
Equi-join – with a join condition that returns only rows with equivalent values
12. What is DML?
We use Data Manipulation Language or DML to access and handle data in the existing objects. The DML statements are select, insert, update, and delete.
RAW datatype in Oracle
The RAW datatype stores variable-length binary data or byte string values. The maximum size for a raw in a table is 32767 bytes.
13. What are Aggregate functions in Oracle?
In an aggregate function, multiple rows or records are combined, and operations performed on a set of values to get a single value as output. Common aggregate functions include:
14. What are Temporal data types?
Time Stamp Datatype
15. What is a View?
View is a logical table based on one or more tables or views. A view does not store data physically. Tables upon which views are based are called Base tables.
16. How are pictures stored onto a database?
Long Raw Data type can be used to store pictures onto a database. Binary data of length 2GB can be stored using this datatype.
17. Where do you use DECODE and CASE statements?
These statements function like the if-then-else statement and are used in Oracle for data value transformation.
18. What is MERGE in Oracle, and how can you merge two tables?
Merge statement allows merging data from two tables subsequently. It selects data from the source table and inserts/updates the data in the destination table as per the condition specified in the query. Merge command is useful in Data warehousing applications.
19. What is NULL value in Oracle?
NULL value indicates missing or unknown data.
Intermediate Oracle Interview Questions
20. What is Integrity Constraint?
Integrity constraint is a declaration to define a business rule for a table column. It ensures data accuracy and consistency. Common types are:
21. What is SQL?
SQL or Structured Query Language is used to communicate with the server for accessing, manipulating, and controlling data.
22. What are the different types of SQL statements?
The five types of SQL statements are:
Data Definition Language (DDL): CREATE, DROP, RENAME, ALTER, TRUNCATE
Data Manipulation Language (DML): INSERT, DELETE, UPDATE, MERGE
Data Control Language (DCL): GRANT, REVOKE
Data Retrieval: SELECT
Transaction Control Statements: COMMIT, SAVEPOINT, ROLLBACK
23. What is PL/SQL?
PL/SQL is an extension of SQL, which is used in Oracle. PL/SQL combines SQL’s data manipulation power with the processing power of procedural language and creates extra-powerful SQL queries. It uses SQL to instruct the compiler what to do and a procedural way to instruct how to do it.
24. What is a Literal?
A Literal is a string consisting of a character, a number, or a date that is included in the Select list but which is not a column name or alias.
25. Difference between SQL and iSQL*Plus?
SQL is a language, but iSQL*Plus is an environment. iSQL*Plus is a command line tool that allows typing SQL commands to be executed directly against the Oracle database. While SQL uses Functions to perform certain formatting, iSQL*Plus uses commands to format data.
26. What are SQL functions?
SQL functions can take arguments but always return a certain value. The 2 types of SQL functions are:
Single-row functions like character, number, date, conversion, and general.
Multiple-row functions like avg, count, sum, max, min, stddev, variance.
Types of SQL General functions are:
27. What is a Sub Query?
A SELECT statement embedded within a clause of another SELECT statement is called a subquery. It can be placed in WHERE, HAVING, and FROM clause.
28. What is VArray?
VArray (variable sized array) is an Oracle datatype used to hold columns containing multi-valued attributes. It can hold a bounded array of values.
Advanced Oracle Interview Questions
29. What is the fastest query method to fetch data from a table?
Using the Row ID is the fastest query method to fetch data from a table.
30. What is the difference between hot backup and cold backup?
Hot backup is also called online backup, as it is done when the database is active.
Cold backup is also called offline backup, as it is done when the database has been shutdown.
31. What are the uses of a database trigger?
Triggers are programs that get automatically executed in response to some events. For example, a trigger can be invoked when a row is inserted into a table. It helps maintain data integrity.
32. What is the difference between TRANSLATE and REPLACE?
TRANSLATE is used to substitute a character by a character, while REPLACE is used to substitute a character with a word.
33. What is Cross Join?
Cross join is the Cartesian product of records from the tables that are there in the join.
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Those were some of the most frequently asked Oracle interview questions. We hope going through the list will help you prepare for your interview and strike a winning chance at landing your dream job. If you wish to get into the depths of Oracle, our Oracle SL course, delivered by top trainers in the field, will help you learn key concepts, advanced techniques, best practices, and real-world applications. You can also choose from our excellent selection of other related courses that will further equip you with the skills needed to build a flourishing career as a web developer. Register with us today!