SQL Group By vs Distinct

Difference between GROUP BY and DISTINCT

GROUP BY is used in combination with aggregation functions. Consider the following table:

orderId	userId	storeName	orderValue	orderDate
1	43	Store A	25	20-03-2016
2	57	Store B	50	22-03-2016
3	43	Store A	30	25-03-2016
4	82	Store C	10	26-03-2016
5	21	Store A	45	29-03-2016

The query below uses GROUP BY to perform aggregated calculations.

SELECT
    storeName,
    COUNT(*) AS total_nr_orders,
    COUNT(DISTINCT userId) AS nr_unique_customers,
    AVG(orderValue) AS average_order_value,
    MIN(orderDate) AS first_order,
    MAX(orderDate) AS lastOrder
FROM
    orders
GROUP BY
    storeName;

and will return the following information

storeName	total_nr_orders	nr_unique_customers	average_order_value	first_order	lastOrder
Store A	3	2	33.3	20-03-2016	29-03-2016
Store B	1	1	50	22-03-2016	22-03-2016
Store C	1	1	10	26-03-2016	26-03-2016

While DISTINCT is used to list a unique combination of distinct values for the specified columns.

SELECT DISTINCT
    storeName,
    userId
FROM
    orders;

storeName	userId
Store A	43
Store B	57
Store C	82
Store A	21