select iif('abcz' similar to '[[:lower:]]{1,}z',1,0) r from rdb$database; -- [1]

select iif('Ab2Z' similar to '[[:alnum:]]{3,}Z',1,0) r from rdb$database; -- [2]

with
d as(
    select 'abcz' text, '[[:lower:]]{1,}z' pattern from rdb$database union all
    select 'Ab2Z',      '[[:alnum:]]{3,}Z'
from rdb$database
)
select d.text, d.pattern, d.text similar to trim(d.pattern) r
from d; --------------------------------------------------------------------- [3]

select 'abcz' similar to '[[:lower:]]{1,}z' r from rdb$database r
union all
select 'Ab2Z' similar to '[[:alnum:]]{3,}Z' from rdb$database; -------------- [4]

select 'abcz' similar to '[[:lower:]]{1,}z' r from rdb$database; ------------ [5]

select 'Ab2Z' similar to '[[:alnum:]]{3,}Z' r from rdb$database; ------------ [6]