Optimizing Second-Highest Salary Query | Dataford Interview Questions

Write a SQL query to find the second-highest salary from an employee table, and then optimize it for a dataset containing millions of rows.

Use the employees table. Treat the second-highest value as the second-highest distinct non-null salary, and ensure duplicate salaries do not affect the result. Address the indexing consideration for a large PostgreSQL table.

Output

Return one row with second_highest_salary.
Return no rows if fewer than two distinct non-null salaries exist.

Schema

employees

Column	Type	Description
employee_idPK	INTEGER	Unique employee identifier
employee_name	VARCHAR(100)	Employee's full name
salary	NUMERIC(12,2)	Employee annual salary
department	VARCHAR(80)	Employee department

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Problem

Write a SQL query to find the second-highest salary from an employee table, and then optimize it for a dataset containing millions of rows.

Output

Return one row with second_highest_salary.
Return no rows if fewer than two distinct non-null salaries exist.

Schema

employees

Column	Type	Description
employee_idPK	INTEGER	Unique employee identifier
employee_name	VARCHAR(100)	Employee's full name
salary	NUMERIC(12,2)	Employee annual salary
department	VARCHAR(80)	Employee department

Your question is Optimizing Second-Highest Salary Query. Start with the requirements and the one table in the Question tab.

Run and submit as often as you like. When you're ready, talk me through your approach or go straight to the code.