How do you integrate Mnesia with QLC for complex queries?

QLC (Query List Comprehension) provides a SQL-like, declarative query syntax over any "queryable" data source, and Mnesia tables can be exposed to it via mnesia:table/1, letting you write joins, sorting, and filtering across one or more tables in a single expression.

mnesia:transaction(fun() ->
    Q = qlc:q([P#person.name || P <- mnesia:table(person), P#person.age > 30]),
    qlc:e(Q)
end).

The real power shows up when joining across multiple tables — something a single select/2 call on one table can't express directly:

Q = qlc:q([{P#person.name, O#order.total} ||
    P <- mnesia:table(person),
    O <- mnesia:table(order),
    P#person.id =:= O#order.person_id]),

QLC queries still need to run inside a transaction (or another activity context) since they ultimately read from Mnesia tables, and QLC handles picking a reasonably efficient evaluation order/plan across the joined sources for you.

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