What is grouping?
Grouping - is arranging observations into sub-groups based on unique values in some column. For example, we can group our audi_cars table by transmission column (contains 3 unique values). There will be observations within each subgroup. So, what's the point of grouping?
In SQL grouping is often used in pair with some aggregate function within SELECT. For example, we can calculate the average price for each transmission type.
SELECT AVG(price), transmission
FROM audi_cars
GROUP BY transmission
SELECT AVG(price), transmission FROM audi_cars GROUP BY transmission
This will return all the transmissions types with average prices within each group.
Tâche
Swipe to start coding
From the audi_cars table calculate the average price of each model. Round price to two decimals.
Solution
SELECT model, ROUND(AVG(price),2)
FROM audi_cars
GROUP BY model
Tout était clair ?
Merci pour vos commentaires !
Section 5. Chapitre 1
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