Why would you use qlc:q with mnesia:table/1 instead of mnesia:select/2?

select/2 is a single-table, match-specification-based query — excellent for filtering one table efficiently, but it can't express a relationship spanning multiple tables in one query. QLC's comprehension syntax reads much closer to how you'd describe the query in plain language (join these two tables, filter, sort), and it can combine several mnesia:table/1 sources in one expression.

%% Multi-table join with QLC
Q = qlc:q([{P#person.name, T#tag.tag} ||
    P <- mnesia:table(person),
    T <- mnesia:table(item_tag),
    P#person.id =:= T#item_tag.item_id]),
qlc:e(Q).

The tradeoff is that QLC's flexibility comes with more overhead than a tightly targeted select/2 call on a single table — for a simple single-table filter, plain select/2 (or even match_object/1) is usually the leaner, faster choice; QLC earns its keep specifically once the query genuinely needs to correlate data across more than one table.

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