Why does 10046 trace show 2 fetch operation while actually fetching 1 row?

Question

Hi all,
As you can see below, query the query returns 1 row, but it seems fetch worked twice.
I wonder why?
Thank you.
select '1'
from
dual
call count cpu elapsed disk query current rows
Parse 1 0.00 0.01 0 0 0 0
Execute 1 0.00 0.01 0 0 0 0
Fetch 2 0.00 0.00 0 0 0 1
total 4 0.00 0.02 0 0 0 1
********************************************************************************

Answer 1

Because you fetched twice ...
For example:
SQL> alter session set events '10046 trace name context forever, level 8'
  2  /
Sessie is gewijzigd.
SQL> declare
  2    cursor c is select '1' from dual;
  3    r c%rowtype;
  4  begin
  5    open c;
  6    fetch c into r;
  7    while c%found
  8    loop
  9      dbms_output.put_line('in loop');
10      fetch c into r;
11    end loop;
12    close c;
13  end;
14  /
in loop
PL/SQL-procedure is geslaagd.
SQL> alter session set events '10046 trace name context off'
  2  /
Sessie is gewijzigd.The above leads to the following tkprof output:
declare
  cursor c is select '1' from dual;
  r c%rowtype;
begin
  open c;
  fetch c into r;
  while c%found
  loop
    dbms_output.put_line('in loop');
    fetch c into r;
  end loop;
  close c;
end;
call     count       cpu    elapsed       disk      query    current        rows
Parse        1      0.04       0.04          0          0          0           0
Execute      1      0.00       0.00          0          0          0           1
Fetch        0      0.00       0.00          0          0          0           0
total        2      0.04       0.04          0          0          0           1
Misses in library cache during parse: 1
Optimizer goal: CHOOSE
Parsing user id: 9833
Elapsed times include waiting on following events:
  Event waited on                             Times   Max. Wait  Total Waited
  ----------------------------------------   Waited  ----------  ------------
  SQL*Net message to client                       1        0.00          0.00
  SQL*Net message from client                     1        0.00          0.00
SELECT '1'
FROM
DUAL
call     count       cpu    elapsed       disk      query    current        rows
Parse        1      0.00       0.00          0          0          0           0
Execute      1      0.00       0.00          0          0          0           0
Fetch        2      0.00       0.00          0          3          0           1
total        4      0.00       0.00          0          3          0           1
Misses in library cache during parse: 1
Optimizer goal: CHOOSE
Parsing user id: 9833     (recursive depth: 1)
Rows     Row Source Operation
      1  TABLE ACCESS FULL DUAL
********************************************************************************Regards,
Rob.