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Description
Submitted by: @dyemanov
Consider this trivial query:
select *
from rdb$relations r
join rdb$relation_fields rf on 1 = 1
Possible plans are:
PLAN JOIN (R NATURAL, RF NATURAL)
and
PLAN JOIN (RF NATURAL, R NATURAL)
but the engine silently ignores any user-specified plan always defaulting to the join order {A -> B} where cardinality(A) < cardinality(B). This isn't always the best choice, however.