In general, common table expressions are useful whenever a table expression must appear multiple times within a single query. The following typical situations are suited to common table expressions.
Queries that involve multiple aggregate functions.
Views within a procedure that must contain a reference to a program variable.
Queries that use temporary views to store a set of values.
This list is not exhaustive; you may encounter many other situations in which common table expressions are useful.
Multiple aggregate functions
Views that reference program variables
Views that store values
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