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It’s often handy to group rows together to count them. For example you could answer the question "How many books are in each genre?"
To count aggregated rows with common values use the GROUP BY keywords:
SELECT COUNT(<column>) FROM <table> GROUP BY <column with common value>;
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Well, we could start out with a query
where we select the category and
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order it by the category.
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We could count all of
these up manually and
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keep track of a tally of each category.
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But there is no need for that.
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I've shown you how to use the Count
function to count all the rows in a table.
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I've also shown you how to use Count
to count the results from a query.
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But for this example, we need to count
the groups of rows by their category.
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For example, all of the clothing products,
all of the electronics products and so on.
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