Hi,
Sequences are used to generate sequential numbers. They are typically used to generate primary key values. Here is an quick example:
SQL> create table tab1(id number primary key, col2 varchar2(30));
Table created.
SQL> create sequence seq1;
Sequence created.
SQL> insert into tab1 values (seq1.nextval, 'Value 1');
1 row created.
SQL> insert into tab1 values (tab1_seq.nextval, 'Value 2');
1 row created.
SQL> select * from tab1;
ID COL2
---------- ------------------------------
1 Value 1
2 Value 2
For more info, read the Oracle SQL Reference Guide.
Best regards.
Frank