Uncorrelated sub-query

A sub-query is another query within a query. The sub-query returns its results to an outer query to be processed.

You want a query that returns the region and countries that have experienced earthquakes centered at a depth of 400km or deeper. Your query will use the Earthquakes table in the sub-query, and Nations table in the outer query.

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Improving Query Performance in SQL Server

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Praktische interactieve oefening

Probeer deze oefening eens door deze voorbeeldcode in te vullen.

SELECT UNStatisticalRegion,
       CountryName 
FROM Nations
WHERE ___ -- Country code for outer query 
         IN (SELECT ___ -- Country code for sub-query
             FROM Earthquakes
             WHERE ___ >= ___ ) -- Depth filter
ORDER BY UNStatisticalRegion;

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