20 Oracle Functions Interview Questions and Answers

Functional programming is a popular programming paradigm that is often used in Oracle databases. If you are applying for a position that involves Oracle databases, it is likely that you will be asked questions about functional programming during your interview. In this article, we review some of the most common Oracle functional programming questions and provide tips on how to answer them.

Oracle Functions Interview Questions and Answers

Here are 20 commonly asked Oracle Functions interview questions and answers to prepare you for your interview:

1. What is a function in Oracle?

A function is a subprogram that is written to perform a specific task. Functions can be written in any language that can be compiled and run on the Oracle database server. Functions can be used to perform calculations, manipulate data, and return information to the caller.

2. How many types of functions are there in Oracle and what are they?

There are two types of functions in Oracle: user-defined functions and built-in functions. User-defined functions are created by the user and can be used in SQL queries. Built-in functions are provided by Oracle and can be used without having to create them first.

3. Can you write an example of creating a simple user-defined function in PL/SQL?

Yes, creating a simple user-defined function in PL/SQL is quite easy. For example, let’s say we wanted to create a function that took in a number and doubled it. We could write this function as follows:

“`
create or replace function double_num (p_num in number)
return number
is
begin
return p_num * 2;
end;
“`

Now, whenever we call this function with a number, it will return that number doubled.

4. What’s the difference between SQRT() and POWER() functions?

The SQRT() function returns the square root of a number, while the POWER() function returns a number raised to a specified power.

5. What’s the main difference between single row and multirow functions?

Single row functions only operate on one row at a time, while multirow functions can operate on multiple rows. Single row functions are typically used for data manipulation, while multirow functions are used for data analysis.

6. When would you consider using a regular expression function for string manipulation?

A regular expression function can be useful for string manipulation when you need to search for a specific pattern within a string, or when you need to replace a specific pattern with another string. For example, if you need to find all instances of the word “cat” within a string, or if you need to replace all instances of the word “cat” with the word “dog”, then a regular expression function would be the appropriate tool for the job.

7. What do you understand about character set conversion functions?

Character set conversion functions are used to convert data from one character set to another. This can be useful when you need to ensure that data is compatible with a particular application or system. For example, you might use a character set conversion function to convert data from Unicode to Latin-1.

8. What does the DECODE() function in SQL do?

The DECODE() function in SQL is used to compare an expression to a set of values, and return a corresponding value based on the result of the comparison. This can be used to provide more granular control over the output of a query, or to simplify complex conditions.

9. What do you understand about data type conversion functions?

Data type conversion functions allow you to convert data from one type to another. This can be useful when you need to store data in a specific format or when you need to compare data that is in different formats.

10. Is it possible to create custom aggregate functions in SQL? If yes, can you explain how?

Yes, it is possible to create custom aggregate functions in SQL. This can be done by using the CREATE AGGREGATE statement. This statement allows you to specify the name of the function, the input data type, the output data type, and the actual function definition.

11. How many ways are there to use the ROUND() function? Which one do you prefer? Why?

There are four ways to use the ROUND() function: ROUND(), ROUNDUP(), ROUNDDOWN(), and TRUNC(). I prefer to use ROUND() because it rounds a number to the nearest integer, which is usually what I am looking for. ROUNDUP() rounds a number up to the nearest integer, ROUNDDOWN() rounds a number down to the nearest integer, and TRUNC() removes the decimal places from a number without rounding it.

12. What is the MAX() function used for?

The MAX() function is used to return the maximum value from a set of values.

13. What is the MIN() function used for?

The MIN() function is used to return the minimum value from a set of values.

14. What are some commonly used date functions in SQL?

Oracle provides a number of date functions that allow you to manipulate dates in SQL. Some of the most commonly used date functions are:

TO_DATE – Converts a string to a date
TO_CHAR – Converts a date to a string
ADD_MONTHS – Adds a specified number of months to a date
LAST_DAY – Returns the last day of the month for a given date

15. What are some common numeric functions in SQL?

Some common numeric functions in SQL are:

ABS(number) – Returns the absolute value of a number
CEIL(number) – Returns the smallest integer greater than or equal to a number
FLOOR(number) – Returns the largest integer less than or equal to a number
MOD(number, divisor) – Returns the remainder of a division operation
ROUND(number, decimal_places) – Rounds a number to a specified number of decimal places

16. How can you rename a column to something more meaningful while querying in SQL?

You can use the AS keyword to rename a column while querying in SQL. For example, if you had a column called “id” that you wanted to rename to “customer_id”, you could use the following SQL:

SELECT id AS customer_id
FROM customers;

17. What is the AVG() function used for?

The AVG() function is used to calculate the average value of a given column.

18. What is the SUM() function used for?

The SUM() function is used to calculate the sum of a given column or expression.

19. What is the COUNT() function used for?

The COUNT() function is used to return the number of rows in a table that meet a certain criteria.

20. What are some advantages of writing stored procedures over adhoc queries?

There are several advantages of writing stored procedures over adhoc queries, including:

– Stored procedures can be reused, so you don’t have to keep rewriting the same code.
– Stored procedures can be optimized for performance, since they are compiled before execution.
– Stored procedures can be used to enforce security, since they can be restricted to only allow certain users to execute them.