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Basic aggregations based on groups of values

SELECT SUM(o_totalprice) AS sum_of_totalprice,
       COUNT(o_totalprice) AS total_number_of_purches,
       AVG(o_totalprice) AS avg_price,
       STDDEV(o_totalprice) AS stddev_from_avg,
       MIN(o_date) AS the_minimum_date,
       MAX(o_date) AS the_maximum_date,
       o_name
FROM orders
GROUP BY o_name
ORDER BY sum_of_totalprice;

Calculates the mathematical aggregations for any given different o_name value.

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Using the aggregation as a subquery

SELECT * FROM orders
WHERE o_totalprice = (SELECT MAX(o_totalprice)
                      FROM orders
                     );

Returns the row with the highest o_totalprice.

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Using the aggregation with no GROUP BY column

SELECT
  SUM((sale_price - purchse_price) * number_of_sold_items) AS total_profit
FROM transactions;

Calculate the total profit of all the different transactions.

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Count by distinct column or expression

SELECT COUNT( DISTINCT c_name) as customers FROM customers;
SELECT COUNT(DISTINCT purchse_price+sale_price) FROM transactions;