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  3. Improving Query Performance in SQL Server

Exercise

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.

Instructions 1/2

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  • Add the country code column to the outer query.
  • Add the country code column to the sub-query.
  • Filter for a depth of 400km or more.