How is the usage of the sequence in Oracle?

In Oracle, a Sequence is an object used to automatically generate unique integer values. It can be used to create unique identifiers for primary key columns in tables, as well as generate unique values for other columns that require them.

Here is how you can use the Sequence method:

1. To create a sequence: You can use the CREATE SEQUENCE statement to create a sequence. The syntax is as follows:
2. Generate a sequence called sequence_name, starting with an initial value, increasing by a specified increment, with a minimum and maximum value, and the option to cycle or not, with a specified cache size.
3. The sequence_name is the name of the sequence. The initial_value is the starting value, defaulting to 1. The increment_value is the step by which the sequence increases, defaulting to 1. The minimum_value and maximum_value are the respective minimum and maximum values of the sequence. CYCLE indicates that the sequence will restart after reaching the maximum value, while NOCYCLE indicates no restart. cache_size represents the number of values cached in memory.
4. Using Sequence: You can use the NEXTVAL function to retrieve the next value of a Sequence, and the CURRVAL function to retrieve the current value. The syntax is as follows:
5. Retrieve the next value or the current value of the sequence called “sequence_name” from the table called “dual”.
6. In this case, sequence_name is the name of the Sequence, while dual is a virtual table used to return a single row result.
7. Using Sequence: You can utilize Sequence in an INSERT statement to generate a unique value, for example:
8. Add a new record to the table with the ID as the next value in the sequence and the name as ‘John’.
9. This ensures that each inserted id value is unique every time.
10. To delete a Sequence, you can use the DROP SEQUENCE statement. The syntax is as follows:
11. Delete the sequence with the name “sequence_name”.
12. sequence_name is the name of the Sequence to be deleted.

It is important to note that a Sequence is a database-level object that can be shared by multiple tables. Additionally, because a Sequence generates values in advance, its values will not be rolled back even if a transaction is rolled back.