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Introduction
Simple CASE WHEN
Searched CASE WHEN
CASE WHEN with aggregates
CASE WHEN with GROUP BY
21. CASE WHEN with GROUP BY – practice 2
Summary

## Instruction

Fine! And yet another one so that you can become the master of GROUP BY with CASE WHEN.

## Exercise

For each degree course, show its ID (as id) and the number of distinct candidates who applied for this course and have the preferred_contact set to:

1. mobile (column: count_mobile),
2. mail (column: count_mail).

### Stuck? Here's a hint!

Things are getting serious. You will need to JOIN two (or three if you'd like) tables this time! Don't forget about the DISTINCT clause.