Commented by: @dyemanov

Some examples of how it could be reported in the detailed query plans:

select count(*) from q;

Select Expression
-> Aggregate
-> Filter
-> Table "Q" Full Scan

select count(*) from q where rdb$db_key > x'8700000001000000';

Select Expression
-> Aggregate
-> Filter
-> Table "Q" Full Scan (lower bound)

select count(*) from q where rdb$db_key <= x'8700000001000000';

Select Expression
-> Aggregate
-> Filter
-> Table "Q" Full Scan (upper bound)

select count(*) from q where rdb$db_key >= x'8700000001000000' and rdb$db_key <= x'8700000005000000';

Select Expression
-> Aggregate
-> Filter
-> Table "Q" Full Scan (lower bound, upper bound)

select count(*) from q where rdb$db_key between x'8700000001000000' and x'8700000005000000';

Select Expression
-> Aggregate
-> Filter
-> Table "Q" Full Scan (lower bound, upper bound)

Commented by: @livius2

Sorry for off topic
but what are a use case for such range queries? Just curious.

Commented by: @dyemanov

Parallel table scans, for example.