SQL And Spark Querying | Dataford Interview Questions

Your question is SQL And Spark Querying. Start with the requirements and the two tables on the right.

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Problem

Context

Exusia's Data Fabric team needs a repeatable way to identify the highest-paid employees while retaining department information when available. The result must handle salary ties and employees whose department reference does not match a department record.

Task

Write a PostgreSQL query that returns every employee earning the maximum salary in the employees table. Also describe how to produce the same result with a DataFrame and an RDD.

Requirements

Use a CTE to calculate the overall maximum non-NULL salary.
Return every employee tied at that salary, including the employee name and salary.
Use a LEFT JOIN to include the employee when its department reference has no matching department.
Order the result by employee name.

Schema

employees

Column	Type	Description
employee_idPK	INT	Unique employee identifier
employee_name	VARCHAR(100)	Employee full name
salary	NUMERIC(12,2)	Annual salary
department_id	INT	Referenced department identifier
job_title	VARCHAR(100)	Current job title

departments

Column	Type	Description
department_idPK	INT	Unique department identifier
department_name	VARCHAR(100)	Department name