Doubt about transaction atomicity

Question

Hello everyone.
Here i am posting some extract from from oracle 10g Documentation "Concepts" manual, "Part Number B10743-01", Chapter 4. "Transcation Managment".
Here are extracts :
"A transaction is a logical unit of work that contains one or more SQL statements. A transaction is an atomic unit. The effects of all the SQL statements in a transaction can be either all committed (applied to the database) or all rolled back (undone from the database)."
Some lines later, this has been given :
"Statement-Level Rollback
If at any time during execution a SQL statement causes an error, all effects of the statement are rolled back. The effect of the rollback is as if that statement had never been run. This operation is a statement-level rollback.
Errors discovered during SQL statement execution cause statement-level rollbacks. An example of such an error is attempting to insert a duplicate value in a primary key. Single SQL statements involved in a deadlock (competition for the same data) can also cause a statement-level rollback. Errors discovered during SQL statement parsing, such as a syntax error, have not yet been run, so they do not cause a statement-level rollback.
A SQL statement that fails causes the loss only of any work it would have performed itself. It does not cause the loss of any work that preceded it in the current transaction. If the statement is a DDL statement, then the implicit commit that immediately preceded it is not undone."
Now, My question is If we are considering TRANSCATION as atomic unit, then whats the relevance of statement level rollback. Moreover, statement level rollback states that if sql statement fails, it causes the loss only of any work it would have performed itself. But in actual, if three statements are fired one after another.
Say, statement 1 and 2 execute successfull but third fails then 1 and 2 also get rollbacked. Which is correct according to fact if we consider transcation as atomic.
But this is not accordance with the statement level rollback (text which is given in bold).
So, any explanation for this. What i am taking wrong.......

Answer 1

SQL> begin
2 insert into test values (1);
3 insert into test values (2);
4 insert into test values (2);
5 end;
6 /
begin
ERROR at line 1:
ORA-00001: unique constraint (SCOTT.SYS_C001481) violated
ORA-06512: at line 4
SQL> select * from test;
no rows selected
See, in this case nothing is inserted in tables, because transcation is atomic.be aware that this result is due solely to the lack of exception handling in your code.
Given this piece of code...
SQL> declare
  2    procedure p (n in number) is
  3    begin
  4      insert into apc1 values (n);
  5      insert into apc1 values (n*2);
  6    exception
  7      when others then null;
  8    end;
  9  begin
10    p(4);
11    p(2);
12  end;
13  /
PL/SQL procedure successfully completed.
SQL>...what rows are currently in the table? Let's take a peek...
SQL> select * from apc1;
      COL1
         4
         8
         2
SQL> In other words, only the last insert failed. This is in accordance with the documentation:
Also, if a stored subprogram fails with an unhandled exception, PL/SQL does not roll back database work done by the subprogram.
In your example all the inserts fail, because you didn't have any exception handling. This was a decision made by your calling environment (I assume SQL*Plus) which does not know how to cope with an unhandled exception except by rolling back the failing statement. Note that it does not rollback the transaction, only the statement...
SQL>  delete from apc1
  2  /
1 row deleted.
SQL> insert into apc1 values (1)
  2  /
1 row created.
SQL> begin
  2     insert into apc1 values (2);
  3     insert into apc1 values (2);
  4  end;
  5  /
begin
ERROR at line 1:
ORA-00001: unique constraint (APC.SYS_C0010124) violated
ORA-06512: at line 3
SQL> select * from apc1
  2  /
      COL1
         1
SQL> Cheers, APC