ORA-62505: expression needs to be aliased

create table tq84_tab (
   id     integer         primary key,
   txt    varchar2(10),
   num    number
);

select
   *
from
   tq84_tab match_recognize (
       order by
          id

       measures
          txt,
          num
          
       pattern (a)
          
       define
          a as length(txt) = num

);

select
   *
from
   tq84_tab match_recognize (
       order by
          id

       measures
          txt as txt,   -- <== Note the alias
          num as num
          
       pattern (a)
          
       define
          a as length(txt) = num

);