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  3. Improving Query Performance in SQL Server

Exercise

Correlated sub-query

Sub-queries are used to retrieve information from another table, or query, that is separate to the main query.

A friend is working on a project looking at earthquake hazards around the world. She requires a table that lists all countries, their continent and the average magnitude earthquake by country. This query will need to access data from the Nations and Earthquakes tables.

Instructions 1/2

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  • Add the average magnitude column in the sub-query.
  • Add the Nations country code column reference in the sub-query.