Execute (or re-execute) commands in the SQL*Plus buffer

Question

I feel confused about sql plus / command. by defination, it Execute (or re-execute) commands in the SQL*Plus buffer. how do I know whether it execete or re-execute a command?
for example, I run a select statement, seems I have to type / to get result. when I run a create table statement, it seems run twice with / and I got table exists error.
Could someone clearify when should / be used and when not to use it.

Answer 1

jz2 wrote:
I feel confused about sql plus / command. by defination, it Execute (or re-execute) commands in the SQL*Plus buffer. how do I know whether it execete or re-execute a command?
for example, I run a select statement, seems I have to type / to get result. when I run a create table statement, it seems run twice with / and I got table exists error.
Could someone clearify when should / be used and when not to use it.I guess you are looking at things in the other way round. The / does what it says, it executes the command in the buffer. Don't think it "reexecutes". It simply executes the command. Be it already run or for the first time. For example,
Running the code for 1st time.
SQL> begin
  2  dbms_output.put_line('hi');
  3  end;
  4  .
SQL> set serveroutput on
SQL> /
hi
PL/SQL procedure successfully completed.
Running again....
SQL> l
  1  begin
  2  dbms_output.put_line('hi');
  3* end;
SQL> /
hi
PL/SQL procedure successfully completed.
SQL>So / simply executes. Now when you should use it and when not, that depends upon the kind of command you are trying to execute. Like you mentioned, for a select, it works by again giving the output. But for a DDL, its not the / which gives error but its the very nature of DDL that once issued, its committed so surely enough , next execution would throw an error only.
HTH
Aman....