From 10g onwards Oracle has had a type of join called a Partitioned Outer Join, providing a convenient syntax which can be used to fill gaps in sparse data.
The documentation describes the result of a partitioned outer join as “a UNION of the outer joins of each of the groups in the logically partitioned table with the table on the other side of the join.”
To demonstrate what this means in practice, I will run through a simple example.
We will start with two very simple tables, products and sales, which look like this:
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