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Filtering group size

Sometimes in real life, you can meet the situation where you have significant differences between two characteristics. For example, the average rate for one item is 5, and for another is 4.6. Without any further analysis looks like that the first item is better, but what if the first item received 2 rates and the second more than a thousand? We need to be ready to this effect.

For example, let's calculate the average price for each model having at least 10 cars in each group.

SELECT model, AVG(price)
FROM audi_cars
GROUP BY model
HAVING COUNT(*) > 10

              
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SELECT model, AVG(price)
FROM audi_cars
GROUP BY model
HAVING COUNT(*) > 10
copy

To calculate the number of observations in each group you can use the known COUNT(*) statement.

Aufgabe

Swipe to start coding

From audi_cars calculate the average price for each engine size (enginesize column). Take into account only groups containing at least 7 observations and sort the resulting table by average price in ascending order.

Lösung

SELECT enginesize, AVG(price)
FROM audi_cars
GROUP BY enginesize
HAVING COUNT(*) >= 7
ORDER BY AVG(price)

War alles klar?

Wie können wir es verbessern?

Danke für Ihr Feedback!

Abschnitt 5. Kapitel 7

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