Creating and Managing Sequences

Sequences are schema objects that generate unique sequential values, which are very useful when you need unique primary keys. The HR schema has three sequences: DEPARTMENTS_SEQ, EMPLOYEES_SEQ, and LOCATIONS_SEQ.

Sequences are used through the pseudocolumns CURRVAL and NEXTVAL, which return the current and next values of the sequence, respectively. After creating a sequence, you must initialize it by using NEXTVAL to get its first value. Only after the sequence is initialized does CURRVAL return its current value.

This section contains:

• Tutorial: Creating a Sequence

• Dropping Sequences