Oracle Interview Questions & Answers

Oracle Interview Questions & Answers

The Questions That You Need to Prepare for Being Successful in An Oracle Interview

You might be getting ready for an Oracle Interview. On the off chance that you are then you should be set up for the meeting with the goal that you can inspire the questioner most. The main thing that you have to do is to be set up with some oracle interview questions. There are some different things too that you should be set up with before you situate yourself in the hot seat anyone would want to be. By perusing the inquiries, you will have the capacity to comprehend what nature of inquiries you can be asked and what might be the right answer in the event that you are asked such a question. There are different arrangements likewise that you have to make before you go for a meeting. You have to arrange the travel subtle elements of yours appropriately. The travel ought to be planned to the point that you don’t be late for the meeting. It is ideal to achieve the scene of the meeting somewhat ahead of schedule than to be late. The following thing is not to be terrified of any circumstance. You may not be sure about a question. In the event that it so happens then require your investment to consider it and after that answer. In the event that you can’t remember the appropriate response, it is ideal to tell the questioner that you don’t have the foggiest idea about the appropriate response than to give a wrong answer. Act naturally amid the meeting. Try not to attempt to mimic others. You should focus on your non-verbal communication. You should have coordinate eye contact with the questioner it will help you to have some certainty. Presently, as you comprehend what to do before and amid the meeting let us see a portion of the inquiries that you might be inquired.

What is the difference between varchar and varchar 2 data types?

This may be the first shell that is exploded by the interviewer. The answer to this question is that the storage capacity of varchar is 2000 bytes while 4000 bytes can be stored in varchar 2. There will be the usage of space for NULL data in varchar but there will no usage of space for NULL data in varchar 2.

For sure this was not the question that you expected to come in the first instance. This is a technique used by the interviewer so as to catch you off guard. So, while you prepare for an interview do not go there with a mindset that you will be asked certain oracle interview questions in a particular sequence. They can ask as they wish and it is your responsibility to be prepared for any question or eventuality. These sets of questions that we are going to discuss will give you ample opportunity to be prepared for such an interview upon Oracle.

Mention the language in which Oracle is developed?

C language is that upon which oracle is developed.

Explain the Raw data type?

The data type which is used for storage of values in a data format that is binary in nature is what Raw Data type is. The maximum size that a table can have Raw data is 32767 bytes.

Explain the usage of NVL function?

When there is the necessity of conversion of NULL values with another or a given set of value then NVL function is used. Like in NVL (Value, replace value).

What is the command used for the calculation of months?

For calculation of months, the command months_ between functions is used. Like Months_ between (Date1, Date2).

Explain nested tables?

The data type that is used in Oracle for supporting columns which contain attributes which are multi-valued. It also holds an entire sub-table.

Are you finding the questions to be very basic? Yes, they are but they are asked for an obvious reason. The interviewer wants to understand the depth of the knowledge that you have regarding oracle. So, do not neglect such types of questions, prepare them thoroughly so that none can find any flaw in the answer that you give.

Explain what is COALESCE function?

This may be the next question that you are asked from the set of oracle interview questions. The answer to this question is that it is the function that is used to return the value which is such that it is set to be not to be NULL in the list that contains it. It may so happen that all the values that are there in the list are NULL then the function will return NULL. COALESCE ( value1, value2,value3,……).

Explain data type BLOB?

It is a binary string that is of varying length and is used for storage of 2 gigabytes of memory. The length of BLOB should be expressed in Bytes.

How are comments represented in oracle?

There are two ways of representation of comments in Oracle. They are:

  • Two dashes(–) before the beginning of the line – Single statement
  • /*—— */ is used to represent it as comments for a block of statement

Can you explain DML?

When you are asked such type of question do not just answer yes I can but explain that. Even if it is not asked to explain you must explain that so that the interviewer cannot ask any further questions upon that. The answer to this question is: The full form of DML is Data Manipulation Language. This is utilized for accessing and manipulating data that are present in the existing objects. The statements of DML are inserted, select, update and delete. It would not implicitly commit the transaction which is current.

Explain the difference between TRANSLATE and REPLACE?

For substitution which is done character by character TRANSLATE is used whereas when you wish to substitute a single character with a word then you use REPLACE.

How do we display rows from the table without duplicates?

For the removal of Duplicate rows, one can use the keyword DISTINCT in the select statement.

The answers may be one liner but they are the ones which are asked to gauge your knowledge. Read through so that you know how to answer these questions in the proper manner.

Explain the usage of the Merge Statement?

When you need to select rows from one or more sources of data for having the required updating and insertion into a table or a view then there is a usage of Merge Statement. The main use of this statement is the combination of multiple operations.

Explain the NULL value in oracle?

Representation of missing or unknown data is called NULL value. They may be used as a place holder or represented in such a manner in default entry to point out that there is no actual data present.

What is the USING Clause and give an example?

The USING clause is utilized to identify with the column to test for parity when there is a joining of two tables.

Select * from employee join salary using employee ID

By doing this the Employee tables join with the Salary tables with the Employee ID.

What is a key preserved table?

When every key of the table can be also the key when there is joining then that table is what a preserved table is. It is guaranteed that only one copy of each row is returned from the base table.

So, how are you feeling till now? Are the questions helpful for the preparation that you need to have for the interview? They must be. We have taken the extreme pain so that we could collect such questions and make them available in front of you so that you do not have to search the net and find them.

Explain what is WITH CHECK OPTION?

The clause that specifies the check level to be done in DML statements is what is WITH CHECK OPTION. The main usage of this is to have the prevention of changes that may occur to a view that would produce results that are not included in the subquery.

Tell what you know about the usage of Aggregate functions in Oracle?

This may be the next question which you are asked from the set of oracle interview questions.

It is a function where the values of numerous rows or accounts are joined together so that it is possible to get a single value output. Frequent aggregate functions are –

  • Average
  • Count
  • Sum

What do you understand by GROUP BY Clause?

A GROUP BY clause can be utilized in a selected statement where it helps in the collection of data across numerous records and clusters where the results are in one or more columns.

What do you understand by subquery and tell about the different types of subqueries?

Sub Query is also named as Nested Query or Inner Query which is utilized to get data from various tables. A subquery is supplemented to the where clause of the main query.

There are two different types of subqueries:

  • Correlated subquery

This nature of subquery cannot be an independent query but can reference columns in a table listed in the list of the outer query.

  • Non-Correlated subquery

They can be treated as an independent query. Results of the subquery that are derived can be submitted to the main query or parent query.

What is a cross join?

It can be defined as the Cartesian product of records from the tables present in the join. The results produced by Cross Join combines every row from the first table with every row from the second table.

These are some of the questions that you may be asked. While you prepare for such an interview try to answer the question yourself then compare it to the answer that is given here. This will enable you to understand where your fault lies. Another thing you must maintain while having the preparation is that you must have a proper schedule for having the preparation. Seat with these questions daily so that as you hear a question you know what to answer. Select a time when you should have practice with these questions. It is good to start beforehand than to seat with these the day before the interview.

Explain temporal data types in Oracle?

Oracle provides the following temporal data types:

  • Date Data Type – Different formats of Dates
  • Time Stamp Data Type – Different formats of Time Stamp
  • Interval Data Type – Interval between dates and time

Explain the creation of privileges in Oracle?

It is nothing but the right to perform an SQL query or to have access to another user object. The presentation of Privilege may be a system privilege or user privilege.


Explain what is VArray?

This is a data type on Oracle that is used for having columns that contain attributes that are multi-valued and they can have abounded array of values.

Explain how it is possible to get field details of a table?

Describe <Table_Name> is utilized to get the field details of a specified table.

Explain the difference between rename and alias?

Rename is the permanent name that is given to a table or a column whereas Alias is the temporary name that is given to a table or column. Rename is not anything but a substitution of name and Alias is nothing but an alternate name of the table or column.

What is a View in Oracle?

It is a logical table that is based on one or more tables or views.  The tables upon which the view is based are called Base Tables and it doesn’t contain data.

Explain what is a cursor variable?

The different statements which can have different values during the run time are what we mean by cursor variable in Oracle. It is a kind of reference type.

Explain what do you mean by cursor attributes?

Every cursor in Oracle has a particular set of attributes that helps an application program to test the state of the cursor. The attributes can be utilized for checking whether the cursor is opened or closed, it is found or not found and also used to find row count.

Explain what are SET operators in Oracle?

These operators can be used with two or more queries. The operators with which it can be used are Union, Union All, Intersect and Minus.

Explain the means of deletion of duplicate rows in a table?

Duplicate rows in the table can be deleted by using ROWID.

Explain what do you understand by integrity constraint?

An integrity constraint is that which is a declaration that defines a set of business rules for a table column. It is used to make certain correctness and constancy of data in a database. There are few types of integrity constraints

  • Domain Integrity
  • Referential Integrity and
  • Domain Integrity

Explain what you understand by an ALERT?

It is a nature of a window that comes up at the center of the screen and overlays a part of the display that is currently there.

What do you understand by a Hash Cluster?

The technique that is utilized for storage of data so that it can be retrieved faster is what I understand by Harsh Cluster. The application of hash value on the table is done for faster retrieval of the rows from the table.

Explain the various constraints used in Oracle?

Following are constraints used:

  • NULL – It is to point to that particular column can contain NULL values
  • NOT NULL – It is to point towards that particular column cannot contain NULL values
  • CHECK – Authenticate that values in the given column to meet the specific criteria
  • DEFAULT – It is to specify the value is assigned to a default value

Mention the difference between SUBSTR and INSTR?

SUBSTR is that which returns specific parts of a string and INSTR is that which provides positioning of character in which a type of pattern is found in a string.

A string is returned by whereas Numeric is returned by INSTR.

What are the different Oracle Database objects?

There are different natures of data objects that can be found in Oracle –

  • Tables – It is a set of elements prearranged in vertical and horizontal
  • Views  – It is a virtual table that is derived from one or more tables
  • Indexes – It is a method of performance tuning that is used for dealing out with the records
  • Synonyms – It is the alias name for tables
  • Sequences – Multiple users can generate unique numbers
  • Table spaces – It is the logical storage unit that is used in Oracle

It must be said that there is flimsiness associated with interviews yet if you can guarantee that you complete your work authentically before going for a meeting you will have the ability to face that with more assurance. Never exhibit your uneasiness or confusion to the examiner. They may blend the words in such a route, to the point that clear request may have all the earmarks of being troublesome. Keep a gathered personality and consider the question and a while later answer that. It can without quite a bit of explanation be said that you know all as to ORACLE so, you can answer any of the oracle interview questions that are hurled at you by the examiner.

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