How to create an Oracle sequence starting with max value from a table?

Question

Trying to create a sequence in Oracle that starts with the max value from a specific table. Why does this not work?

CREATE SEQUENCE transaction_sequence
  MI         


        

Answer 1

you might want to start with max(trans_seq_no) + 1.

watch:

SQL> create table my_numbers(my_number number not null primary key);

Table created.

SQL> insert into my_numbers(select rownum from user_objects);

260 rows created.

SQL> select max(my_number) from my_numbers;

MAX(MY_NUMBER)
--------------
           260

SQL> create sequence my_number_sn start with 260;

Sequence created.

SQL> insert into my_numbers(my_number) values (my_number_sn.NEXTVAL);
insert into my_numbers(my_number) values (my_number_sn.NEXTVAL)
*
ERROR at line 1:
ORA-00001: unique constraint (NEIL.SYS_C00102439) violated

When you create a sequence with a number, you have to remember that the first time you select against the sequence, Oracle will return the initial value that you assigned it.

SQL> drop sequence my_number_sn;

Sequence dropped.

SQL> create sequence my_number_sn start with 261;

Sequence created.

SQL>  insert into my_numbers(my_number) values (my_number_sn.NEXTVAL);

1 row created.

If you're trying to do the 'gapless' thing, I strongly advise you to

1 not do it, and #2 not use a sequence for it.