GROUP BY - little gem for aggregating data

When you need to count (or sum, or aggregate) data and see the results "for each of something", then GROUP BY is probably what you want.

Note: you have to make sure that the SELECT columns appear in the GROUP BY clause - up to the last aggregator.

From W3Schools.com:

The GROUP BY statement is used in conjunction with the aggregate functions to group the result-set by one or more columns.

SQL GROUP BY Syntax

SELECT column_name, aggregate_function(column_name)
FROM table_name
WHERE column_name operator value
GROUP BY column_name
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