For what are "CREATE SEQUENCE ... INCREMENT BY 1 START WITH 1" ?

Question

I have seen SQL statements for Oracle Databases in the form like
CREATE SEQUENCE sq_ordernum INCREMENT BY 1 START WITH 1
For what are these kind of statements and how can I access/use them?
Peter

Answer 1

sequence is used to increment a number when ever you use seq.next val;
SQL> CREATE SEQUENCE sq_ordernum INCREMENT BY 1 START WITH 1
  2  /
Sequence created.
SQL> select sq_ordernum.nextval from dual;
   NEXTVAL
         1
SQL> select sq_ordernum.nextval from dual;
   NEXTVAL
         2
SQL> select sq_ordernum.nextval from dual;
   NEXTVAL
         3
SQL> select sq_ordernum.nextval from dual;
   NEXTVAL
         4
SQL> select sq_ordernum.nextval from dual;
   NEXTVAL
         5
SQL> select sq_ordernum.currval from dual;
   CURRVAL
         5
SQL>