GROUP BY

Returns queries in groups

SELECT SALES_DATE, SUM(TOTAL_AMOUNT)
FROM SALES
GROUP BY SALES_DATE
ORDER BY SALES_DATE;

This will take the sales made on the dates add them and return a column with the date -> total amount

Grouping Data using Multiple Columns

SELECT SALES_DATE, PRODUCT_ID, SUM(TOTAL_AMOUNT)
FROM SALES
WHERE SALES_DATE BETWEEN '01-JAN-15' AND '31-JAN-15'
GROUP BY SALES_DATE, PRODUCT_ID;

Ex: a report containing total sales volume for January group by day and product