Learn Standard SQL Functions | Interactive Course | Vertabelo Academy

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11/37 COUNT and GROUP BY – additional practice

1. Introduction

2. Table translator

3. Table project

4. Count all rows

5. COUNT with column

6. COUNT(*) vs. COUNT(column) – practice

7. COUNT with expression

8. COUNT DISTINCT

9. COUNT DISTINCT with expression

10. COUNT and GROUP BY

11. COUNT and GROUP BY – additional practice

12. COUNT DISTINCT and GROUP BY

13. COUNT DISTINCT with expression and GROUP BY

14. Common mistake: COUNT(*) and LEFT JOIN

15. COUNT – additional exercise 1

16. COUNT – additional exercise 2

17. Function AVG

18. AVG and GROUP BY

19. AVG and NULLs

20. AVG and NULLs only

21. AVG with COALESCE

22. COALESCE with AVG

23. AVG and DISTINCT

24. ROUND and AVG

25. AVG – additional exercise

26. Function SUM

27. SUM with NULLs only

28. SUM and COALESCE

29. SUM and DISTINCT

30. MAX and MIN

31. SUM, MAX and MIN – exercise

37. Congratulations

Good! Of course, you can use COUNT(*), COUNT(column), or COUNT(expression) with GROUP BY.

For each project, show the client_id and the number of projects commissioned by that specific client which have some feedback (zero if there are no such projects). Name the second column projects_no.

Remember to use COUNT(feedback) instead of COUNT(*).

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