Write queries to compute salary and budget stats

You are given the following interview tasks. Write solutions in SQL and/or Python (pandas) as appropriate.

Task 1 — Second highest salary

You have a table:

employees

• employee_id INT (PK)
• name VARCHAR
• salary INT

Return the second highest distinct salary.

• If there is no second distinct salary, return NULL.

Required output

• second_highest_salary (INT or NULL)

Task 2 — Merge two datasets

You are given two datasets that share a common key:

users

• user_id INT (PK)
• country VARCHAR
• signup_date DATE

user_events

• user_id INT (FK → users.user_id)
• event_time TIMESTAMP
• event_type VARCHAR

Merge them so that each event row is enriched with user attributes.

• Keep only events that have a matching user_id in users (inner join).

Required output

• user_id, country, signup_date, event_time, event_type

Task 3 — “Run out the budget” (maximize hires)

You have a list/table of employees with their salaries and a total hiring budget B.

• Each employee costs exactly their salary.
• You can hire at most once per employee.
• Goal: maximize the number of employees hired without exceeding the budget.

Input

• employees(employee_id, salary) and an integer B

Required output

• max_hires (INT)

Clarify any assumptions you need (e.g., what to do if B <= 0).