I am not sure whether some tuning guy at Oracle decided to ignore any SELECT statement after execute immediate to save time doing nothing.

exec execute immediate 'select 1/0 from dual connect by level<9999999999999'

PL/SQL procedure successfully completed.

Elapsed: 00:00:00.00

But it is really annoying… and not documented as far as I know.

Imagine I want to increase all my sequences by 1000

SQL> create sequence s;

Sequence created.

SQL> select s.nextval from dual;

   NEXTVAL
----------
         1

SQL> begin
  2    for f in (select sequence_name n from user_sequences)
  3    loop
  4      execute immediate
  5        'select '||f.n||'.nextval from dual connect by level<=1000';
  6    end loop;
  7  end;
  8  /

PL/SQL procedure successfully completed.

SQL> select s.currval from dual;

   CURRVAL
----------
         1

Hmm, it does not work. Does SELECT work at all? Yes when it is a SELECT INTO

SQL> drop sequence s;

Sequence dropped.

SQL> create sequence s;

Sequence created.

SQL> select s.nextval from dual;

   NEXTVAL
----------
         1

SQL> declare
  2    type t is table of number index by pls_integer;
  3    c t;
  4  begin
  5    for f in (select sequence_name n from user_sequences)
  6    loop
  7      execute immediate
  8        'select '||f.n||'.nextval from dual connect by level<=1000'
  9        bulk collect into c;
 10    end loop;
 11  end;
 12  /

PL/SQL procedure successfully completed.

SQL> select s.currval from dual;

   CURRVAL
----------
      1001

I wonder in which version this optimization/bug was introduced…