Oracle 18c

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CREATE TYPE a_obj IS OBJECT (
  a1 INTEGER,
  a2 integer
);
CREATE TABLE a OF a_obj (
  CONSTRAINT a__a1__pk PRIMARY KEY (a1)
);
insert into a (a1,a2) values (1,2);
1 rows affected

select a_obj(a.a1,a.a2) from a;
declare 
  ret a_obj;
begin
  select a_obj(a.a1,a2) into ret
  from a;
end;
/
1 rows affected

select a_obj(a.*) from a;
ORA-01747: invalid user.table.column, table.column, or column specification

declare 
  ret a_obj;
begin
  select a.* into ret
  from a;
end;
/
ORA-06550: line 5, column 3:
PL/SQL: ORA-00947: not enough values
ORA-06550: line 4, column 3:
PL/SQL: SQL Statement ignored

select a.OBJECT_VALUE from a;
declare 
  ret a_obj;
begin
  select a.OBJECT_VALUE into ret
  from a;
end;
/
1 rows affected