LEFT JOIN
mixed with grouping and counting is the basis for histogram analysis. Number of readers per books is just one of the examples 
Since LEFT JOIN
keeps all records from the left table weâll have all of them in our distribution, even if they have no associated records in the right table.
Letâs finish our example with counting readers per book:
SELECT * FROM books b LEFT JOIN books_users u ON u.book_id = b.id
Unlike in a joined table with INNER JOIN
some of the right table records are just NULL
-s
If we run our typical grouping and...
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