what is the most complex sql query you have written till date. Why did you use nested query to achieve your goal? explain the query. which join did you use in the query. have you implemented hashset? how will you implement the contains() function of hashset without using the inbuilt functionality? What property of trees makes you not use trees? if a linked list is ordered what is it's tree traversal time going to be? how do you avoid the drawbacks of trees?