Why my system hanged when i execute this block

Question

when i execute this query , why my oracle stop reponding
and after some time start an ifinite output...
declare
v_nextval varchar2(10);
cursor c6 is
(select seq_a.nextval from dual);
begin
open c6;
loop
fetch c6 into v_nextval ;
exit when v_nextval <= 10;
dbms_output.put_line(v_nextval);
end loop;
close c6;
end;
kinkly take a look on this
thanks

Answer 1

Maybe something like this.
>
suppose in my table col A
have last inserted value 258
i have migrated database from sql server 2005 to oracle 10g
where sequences currval is not initailized and last value is 1
now i m creating a new sequence but i do not want to mention Startwith 258
so how to do
>
SQL> select 'create sequence sequence_' || chr(level + 64)  || ' start with 1 ; ' from dual
  2  connect by level <= 2;
'CREATESEQUENCESEQUENCE_'||CHR(LEVEL+64)||'ST
create sequence sequence_A start with 1 ;
create sequence sequence_B start with 1 ;
SQL> create sequence sequence_A start with 1 ;
Sequence created.
SQL> create sequence sequence_B start with 1 ;
Sequence created.
SQL> create table table_A
  2  (
  3   sno number
  4  )
  5  /
Table created.
SQL>
SQL> insert into table_a
  2  select level from dual connect by level <= 10;
10 rows created.
SQL>
SQL> create table table_b
  2  (
  3   sno number
  4  )
  5  /
Table created.
SQL>
SQL>
SQL> insert into table_b
  2  select level from dual connect by level <= 20;
20 rows created.
SQL> with mapping_table
  2  as
  3  (
  4   select 'sequence_a' sequence_name, 'table_a' tname, 'sno' column_name from dual
  5   union all
  6   select 'sequence_b', 'table_b', 'sno' from dual
  7  ),
  8  max_value_table
  9  as
10  (
11   SELECT
12       sequence_name,
13       to_number(
14         extractvalue(
15           xmltype(
16    DBMS_XMLGEN.getxml('select max(' || column_name || ') c from '||tname))
17           ,'/ROWSET/ROW/C')) max_value
18  FROM mapping_table
19  )
20  select * from max_value_table;
SEQUENCE_N  MAX_VALUE
sequence_a         10
sequence_b         20
  1* select * from user_sequences where sequence_name in ('SEQUENCE_A','SEQUENCE_B')
SQL> /
SEQUENCE_NAME                   MIN_VALUE  MAX_VALUE INCREMENT_BY C O CACHE_SIZE LAST_NUMBER
SEQUENCE_A                              1 1.0000E+27            1 N N         20           1
SEQUENCE_B                              1 1.0000E+27            1 N N         20           1
SQL> with mapping_table
  2  as
  3  (
  4   select 'sequence_a' sequence_name, 'table_a' tname, 'sno' column_name from dual
  5   union all
  6   select 'sequence_b', 'table_b', 'sno' from dual
  7  ),
  8  max_value_table
  9  as
10  (
11   SELECT
12       sequence_name,
13       to_number(
14         extractvalue(
15           xmltype(
16    DBMS_XMLGEN.getxml('select max(' || column_name || ') c from '||tname))
17           ,'/ROWSET/ROW/C')) max_value
18  FROM mapping_table
19  ) ,
20  sequence_collation
21  as
22  (
23   select us.sequence_name, us.increment_by, mvt.max_value from user_sequences us, max_value_Table mvt
24   where
25       us.sequence_name = upper(mvt.sequence_name)
26  ),
27  sequence_exec_order
28  as
29  (
30  select 1 execution_sequence, 'alter sequence ' || sequence_name || ' increment by ' || max_value || ';' text from sequence_collation
31  union all
32  select 2, 'select ' || sequence_name || '.nextval from dual ; ' from sequence_collation
33  union all
34  select 3, 'alter sequence ' || sequence_name || ' increment by ' || increment_by || ' ;' from sequence_collation
35  )
36  select text from sequence_exec_order order by execution_sequence
37  /
TEXT
alter sequence SEQUENCE_A increment by 10;
alter sequence SEQUENCE_B increment by 20;
select SEQUENCE_A.nextval from dual ;
select SEQUENCE_B.nextval from dual ;
alter sequence SEQUENCE_A increment by 1 ;
alter sequence SEQUENCE_B increment by 1 ;
6 rows selected.
SQL> alter sequence SEQUENCE_A increment by 10;
Sequence altered.
SQL> alter sequence SEQUENCE_B increment by 20;
Sequence altered.
SQL> select SEQUENCE_A.nextval from dual ;
   NEXTVAL
        10
SQL> select SEQUENCE_B.nextval from dual ;
   NEXTVAL
        20
SQL> alter sequence SEQUENCE_A increment by 1 ;
Sequence altered.
SQL> alter sequence SEQUENCE_B increment by 1 ;
Sequence altered.
SQL> select * from user_sequences where sequence_name in ('SEQUENCE_A','SEQUENCE_B')
  2  /
SEQUENCE_NAME                   MIN_VALUE  MAX_VALUE INCREMENT_BY C O CACHE_SIZE LAST_NUMBER
SEQUENCE_A                              1 1.0000E+27            1 N N         20          11
SEQUENCE_B                              1 1.0000E+27            1 N N         20          21Regards
Raj
P.S : dbms_xmlgen query from the old posts in this forum.....