OLX Software Developer Interview Questions and Answers

Design a database schema for a chat application with individual and group messaging.

• Create a 'users' table with unique user IDs

• Create a 'messages' table with message IDs, sender and receiver IDs, message content, and timestamp

• Create a 'groups' table with unique group IDs and group names

• Create a 'group_members' table with group ID and user ID to track group membership

• Use foreign keys to link tables together

• Consider indexing frequently queried columns for performance

SQL query to retrieve all unread messages upon user sign in

• Use a JOIN statement to combine the messages and user tables

• Filter the results to only show messages that have not been read by the user

• Use the user's sign in information to identify which messages are unread

Our website receives an average of 10,000 unique visitors per day.

• Our website has a steady flow of traffic with a consistent number of unique visitors per day.

• We use Google Analytics to track our web traffic and analyze user behavior.

• Our peak traffic times are during weekdays from 9am to 5pm.

• We have noticed an increase in mobile traffic over the past year.

• Our website's traffic is primarily driven by organic search and social media.

To find missing number in an array of first n numbers.

• Calculate the sum of first n numbers using formula n*(n+1)/2

• Calculate the sum of given array using loop

• Subtract the sum of array from sum of first n numbers to get the missing number

include_once and require_once are PHP functions used to include files. The difference is in how they handle errors.

• include_once will only include the file once, and will not throw a fatal error if the file is not found

• require_once will also only include the file once, but will throw a fatal error if the file is not found

• Both functions are used to include files that contain functions or variables that are needed in the current script

Sessions and cookies are both used for maintaining user state, but sessions are server-side and cookies are client-side.

• Sessions store user data on the server, while cookies store data on the client's browser

• Sessions are more secure than cookies because the data is not accessible to the client

• Cookies can be used for tracking user behavior and preferences

• Sessions are typically used for authentication and authorization purposes

• Cookies can be set to expire after a certain amount...read more