How to change the Oracle Sequence using loop? - oracle

Question

Hope someone can help. When I tried to insert something into a table it give me error saying the primary key is already existed. So I need to reset my sequence so that it is always max(id)+1.
The table is called 'People' with 2 columns (ID, Name). The sequence is called SEQ.
I am thinking of doing a loop. To run select SEQ.nextval from dual for n times. this n= max(id)-SEQ.currval
Wwill this work? and how Can I put it into the syntax?
Thanks a lot.

Answer 1

declare
l_MaxVal pls_integer;
l_Currval pls_integer default - 1;
begin
select max(id)
into l_MaxVal
from people;
while l_Currval < l_Maxval
loop
select my_seq.nextval
into l_Currval
from dual;
end loop;
end;

Answer 2

If this is a one off, you can use the alter sequence
alter sequence sequenceName increment by val ;
whereas val is +1 to the maximum
then call get nextVal, then set the increment back to 1.
I threw the below together to show you how it can be done without looping.
create sequence changeValue start with 18 increment by 1 nocache ;
select changeValue.nextval from dual ;
/
NEXTVAL
----------------------
18
set serveroutput on
declare
maxVal number := 24 ;
curVal number ;
diffVal number ;
incrementVal number ;
procedure alterSequence(seqName in varchar2, incVal in number) as
s varchar2(500);
begin
s := 'alter sequence ' || seqName || ' increment by ' || incVal ;
dbms_output.put_line(s);
execute immediate s;
end alterSequence;
begin
--(done in 11gr2 so if in earlier version select into)
curVal := changeValue.currval ;
dbms_output.put_line('curValue=>' || curVal );
diffVal := maxVal - curVal ;
dbms_output.put_line('diffVal=>' || diffVal );
alterSequence ( 'changeValue' , diffVal + 1 );
incrementVal := changeValue.nextval ;
dbms_output.put_line('incrementVal=>' || incrementVal );
alterSequence ( 'changeValue' , 1 );
curVal := changeValue.currval ;
dbms_output.put_line('curValue=>' || curVal );
end ;
/
curValue=>18
diffVal=>6
alter sequence changeValue increment by 7
incrementVal=>25
alter sequence changeValue increment by 1
curValue=>25
or better yet, as #Dave suggests, just drop and recreate the sequence with the acceptable Start With value.

Answer 3

With this one you can synchronize the sequence whatever it is forward or behind the max of the ID.
Just need to change the parameters in the final of the code.
declare
procedure SYNC_SEQUENCE
( P_IN_SEQ in varchar2
, P_IN_TABLE in varchar2
, P_IN_ID in varchar2
)
is
LV_MAXVAL number := 0;
LV_CURRVAL number := -1;
LV_AUX NUMBER;
begin
execute immediate
'select max('||P_IN_ID||')
from '||P_IN_TABLE into LV_MAXVAL;
execute immediate
'select '||P_IN_SEQ||'.nextval
from dual ' into LV_CURRVAL;
if LV_MAXVAL < LV_CURRVAL then
LV_AUX := (LV_CURRVAL - LV_MAXVAL);
execute immediate
'ALTER SEQUENCE '||P_IN_SEQ||' INCREMENT BY -'||LV_AUX;
execute immediate
'SELECT '||P_IN_SEQ||'.NEXTVAL FROM dual' INTO LV_AUX;
execute immediate
'ALTER SEQUENCE '||P_IN_SEQ||' INCREMENT BY 1';
end if;
while LV_CURRVAL < LV_MAXVAL
loop
execute immediate
'select '||P_IN_SEQ||'.nextval
from dual ' into LV_CURRVAL;
end loop;
end SYNC_SEQUENCE;
begin
SYNC_SEQUENCE('MY_SEQUENCIE_NAME','MY_TABLE_NAME','MY_FIELD_ID_NAME');
end;
/