How do I reset a sequence in Oracle?

Here is a good procedure for resetting any sequence to 0 from Oracle guru Tom Kyte. Great discussion on the pros and cons in the links below too.

tkyte@TKYTE901.US.ORACLE.COM> 
create or replace
procedure reset_seq( p_seq_name in varchar2 )
is
    l_val number;
begin
    execute immediate
    'select ' || p_seq_name || '.nextval from dual' INTO l_val;

    execute immediate
    'alter sequence ' || p_seq_name || ' increment by -' || l_val || 
                                                          ' minvalue 0';

    execute immediate
    'select ' || p_seq_name || '.nextval from dual' INTO l_val;

    execute immediate
    'alter sequence ' || p_seq_name || ' increment by 1 minvalue 0';
end;
/

From this page: Dynamic SQL to reset sequence value
Another good discussion is also here: How to reset sequences?

A true restart is not possible AFAIK. (Please correct me if I'm wrong!).

However, if you want to set it to 0, you can just delete and recreate it.

If you want to set it to a specific value, you can set the INCREMENT to a negative value and get the next value.

That is, if your sequence is at 500, you can set it to 100 via

ALTER SEQUENCE serial INCREMENT BY -400;
SELECT serial.NEXTVAL FROM dual;
ALTER SEQUENCE serial INCREMENT BY 1;

This stored procedure restarts my sequence:

Create or Replace Procedure Reset_Sequence  
  is
  SeqNbr Number;
begin
   /*  Reset Sequence 'seqXRef_RowID' to 0    */
   Execute Immediate 'Select seqXRef.nextval from dual ' Into SeqNbr;
   Execute Immediate 'Alter sequence  seqXRef increment by - ' || TO_CHAR(SeqNbr) ;
   Execute Immediate 'Select seqXRef.nextval from dual ' Into SeqNbr;
   Execute Immediate 'Alter sequence  seqXRef increment by 1';
END;

/

1) Suppose you create a SEQUENCE like shown below:

CREATE SEQUENCE TESTSEQ
INCREMENT BY 1
MINVALUE 1
MAXVALUE 500
NOCACHE
NOCYCLE
NOORDER

2) Now you fetch values from SEQUENCE. Lets say I have fetched four times as shown below.

SELECT TESTSEQ.NEXTVAL FROM dual
SELECT TESTSEQ.NEXTVAL FROM dual
SELECT TESTSEQ.NEXTVAL FROM dual
SELECT TESTSEQ.NEXTVAL FROM dual

3) After executing above four commands the value of the SEQUENCE will be 4. Now suppose I have reset the value of the SEQUENCE to 1 again. The follow the following steps. Follow all the steps in the same order as shown below:

1. ALTER SEQUENCE TESTSEQ INCREMENT BY -3;
2. SELECT TESTSEQ.NEXTVAL FROM dual
3. ALTER SEQUENCE TESTSEQ INCREMENT BY 1;
4. SELECT TESTSEQ.NEXTVAL FROM dual

Altering the sequence's INCREMENT value, incrementing it, and then altering it back is pretty painless, plus you have the added benefit of not having to re-establish all of the grants as you would had you dropped/recreated the sequence.

Stored procedure that worked for me

create or replace
procedure reset_sequence( p_seq_name in varchar2, tablename in varchar2 )
is
    l_val number;
    maxvalueid number;
begin
    execute immediate 'select ' || p_seq_name || '.nextval from dual' INTO l_val;
    execute immediate 'select max(id) from ' || tablename INTO maxvalueid;
    execute immediate 'alter sequence ' || p_seq_name || ' increment by -' || l_val || ' minvalue 0';
    execute immediate 'select ' || p_seq_name || '.nextval from dual' INTO l_val;
    execute immediate 'alter sequence ' || p_seq_name || ' increment by '|| maxvalueid ||' minvalue 0';  
    execute immediate 'select ' || p_seq_name || '.nextval from dual' INTO l_val;
    execute immediate 'alter sequence ' || p_seq_name || ' increment by 1 minvalue 0';
end;

How to use the stored procedure:

execute reset_sequence('company_sequence','company');