Lesson 5 of 15 · 18 min
RIGHT and FULL OUTER JOIN
By the end of this lesson you can rewrite a RIGHT JOIN as a LEFT JOIN, use FULL OUTER JOIN to reconcile two lists, and merge the keys of both sides with COALESCE.
RIGHT JOIN: the mirror image
A RIGHT JOIN keeps every row of the right table (the one after the keyword) and fills the left side with NULL when there is no match. That is all: A RIGHT JOIN B returns the same rows as B LEFT JOIN A, with the columns in a different order.
Because the two are interchangeable, most teams write LEFT JOINs only: the table whose rows must all survive goes first, and a reader can follow a long query top to bottom without flipping directions. You still need to read RIGHT JOIN, because generated SQL and older reports use it.
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