SQL Quest › SQL Interview Questions › Aggregation & Grouping
How Many Genres Do We Cover? (DISTINCT)
A content programming meeting needs a one-number answer: how many distinct genres does the catalog contain?
Show a single value as unique_genres.
COUNT(DISTINCT col) counts the number of unique non-NULL values. COUNT(col) counts non-NULL rows (with duplicates), COUNT(*) counts all rows (NULLs included). Knowing the three is the difference between a right number and a slightly-wrong number nobody catches until the meeting.
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Schema
movies
| id | title | year | genre | rating | votes | revenue_millions | runtime | director |
|---|---|---|---|---|---|---|---|---|
| 1 | Guardians of the Galaxy | 2014 | Action | 8.1 | 757074 | 333.13 | 121 | James Gunn |
| 2 | Prometheus | 2012 | Adventure | 7 | 485820 | 126.46 | 124 | Ridley Scott |
| 3 | Split | 2016 | Horror | 7.3 | 157606 | 138.12 | 117 | M. Night Shyamalan |
Expected output: unique_genres = 3
Hint
SELECT, COUNT, DISTINCT, and open the hint there if you stall.Concepts
SELECT COUNT DISTINCT Aggregation
Practise the topic: SQL practice questions · GROUP BY exercises
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