Diagnosing problems using anti-join
Another powerful join in SQL is the anti-join. It is particularly useful in identifying which records are causing an incorrect number of records to appear in join queries.
You will also see another example of a subquery here, as you saw in the first exercise on semi-joins. Your goal is to identify the currencies used in Oceanian countries!
Example
.....Note that not all countries in Oceania were listed in the resulting inner join with currencies
. Use an anti-join to determine which countries were not included!