Every subquery has an outer query that it belongs to. Self-contained subqueries are subqueries that
are independent of the outer query that they belong to. Self-contained subqueries are very conve-
nient to debug, because you can always highlight the subquery code, run it, and ensure that it does
what it’s supposed to do. Logically, it’s as if the subquery code is evaluated only once before the outer
query is evaluated, and then the outer query uses the result of the subquery. The following sections
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Microsoft SQL Server 2012 T-SQL Fundamentals
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