Sams Teach Yourself SQL in 10 Minutes, Second Edition

Combining Aggregate Functions

All the examples of aggregate function used thus far have involved a single function. But actually, SELECT statements may contain as few or as many aggregate functions as needed. Look at this example:

SELECT COUNT(*) AS num_items,
    MIN(prod_price) AS price_min,
    MAX(prod_price) AS price_max,
    AVG(prod_price) AS price_avg
FROM Products;

num_items    price_min          price_max          price_avg
----------   ---------------    ---------------    ---------
9            3.4900             11.9900            6.823333

Here a single SELECT statement performs four aggregate calculations in one step and returns four values (the number of items in the Products table, and the highest, ...