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GROUP BY Extensions in PostgreSQL

Introduction
GROUP BY – Recap
Summary
20. Exercise 2

Instruction

Perfect! One more exercise!

Exercise

Show the sum of the total_cost for each department and year, and the total sum of total_cost for each year. Do not show the grand total.

Show the following columns: department, year, and the sum of total_cost (as total). Instead of NULLs in the department column, show the following text: 'unknown'.

Make sure that your table consists of the following columns: department, year, and total.