ORA-01748: only simple column names allowed here

create table tq84_ora_01748 (
   x.y varchar2(10)
);

create table tq84_tab(
   col_1    integer,
   col_2    varchar2(5),
   val_foo  number(4,1),
   val_bar  number(4,1),
   val_baz  number(4,1)
);


select
   *
from
   tq84_tab unpivot (
     val for txt in (
         tab.val_foo as 'Foo',  <-- tab.… causes ORA-01748: only simple column names allowed here
         tab.val_bar as 'Bar',
         tab.val_baz as 'Baz'
     )
   ) tab 
;


--
-- Better:
--
select
   *
from
  tq84_tab unpivot (
     val for txt in (
         val_foo as 'Foo',
         val_bar as 'Bar',
         val_baz as 'Baz'
     )
  ) tab 
;


drop table tq84_tab;