As the workhorse of data analytics and reporting, the SQL language enables both users and developers slice-and-dice a database for desired information.  With a natural-language-based syntax, SQL is relatively easy for business analysts to learn for basic database analysis.  As analysts become more comfortable with the language, however, they may require more advanced techniques, such as aggregates on subsets of data within a query.  In these situations, correlated subqueries can bring new capability and virtually unlimited depth to a SQL statement.
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