What is Session in PHP? How can we refresh a Session in PHP? What are Cookies? Why they are used? What is the difference between Session and Cookies? How we can implement the login and logout functionality in our web application? How would you define a variable in Session? What is the Explode() function? What is an Array? How many types of Array are there in PHP? Name some methods related to the array. What is a Variable? How we can define a variable. Write a function to find the Odd & Even of the given number. (Machine Coding) What a function to get the sum of values(Integer) stored in a variable as Strings. (Machine Coding) What is Indexing in MySQL? Why indexing is used? How does indexing work and why is it useful? What is Primary Key and Foreign Key? Can we make multiple primary keys in a table(RDBMS)?