CYCLE FAQS

1. What is the purpose of the CYCLE option in Oracle sequences?

• The CYCLE option allows an Oracle sequence to restart from its initial START WITH value when it reaches its MAXVALUE (for ascending sequences) or MINVALUE (for descending sequences). This enables the sequence to continue generating values in a loop instead of throwing an error when the sequence reaches its boundary.

2. What happens if CYCLE is not specified?

• If CYCLE is not specified, the sequence defaults to NOCYCLE, meaning once the sequence reaches its MAXVALUE (ascending sequence) or MINVALUE (descending sequence), it will stop and not generate further values, raising an error on the next NEXTVAL call.

3. Can I use CYCLE with both ascending and descending sequences?

• Yes, CYCLE can be used with both ascending and descending sequences:
• For an ascending sequence, it wraps around to the START WITH value once the MAXVALUE is reached.
• For a descending sequence, it wraps around to the START WITH value (or MAXVALUE in some cases) once the MINVALUE is reached.

4. What happens if a sequence with CYCLE exceeds its MAXVALUE or MINVALUE?

• When the sequence reaches its MAXVALUE (for ascending sequences) or MINVALUE (for descending sequences) and CYCLE is enabled, it will restart from the START WITH value, creating a cyclic pattern.

5. Can I modify an existing sequence to use CYCLE after it has been created?

• No, once a sequence is created, you cannot alter the CYCLE option. To modify it, you would need to drop the sequence and recreate it with the desired option.

6. What is the default behavior of Oracle sequences if CYCLE is not used?

• By default, Oracle sequences use NOCYCLE, meaning once the sequence reaches the MAXVALUE (ascending) or MINVALUE (descending), it stops generating further values and an error occurs when NEXTVAL is called.

7. What is the maximum value of a sequence when using CYCLE?

• The MAXVALUE for an ascending sequence and the MINVALUE for a descending sequence is limited by the datatype used for the sequence (e.g., NUMBER or INTEGER). For most common sequences, the MAXVALUE can be set to a large number, but the value must be within the range that the datatype allows.

8. Can I specify a non-numeric sequence with CYCLE?

• No, CYCLE applies only to numeric sequences. Non-numeric values (like strings or custom types) cannot be cycled in Oracle sequences.

9. Is CYCLE useful for creating unique identifiers?

• CYCLE can be useful in cases where you need a repeating series of numbers or identifiers, like round-robin allocations. However, if you need unique identifiers that never repeat, you should avoid using CYCLE.

10. Can I specify both CYCLE and START WITH values?

• Yes, you can specify CYCLE and a START WITH value in the same sequence. The sequence will restart from the START WITH value after reaching the MAXVALUE or MINVALUE.

11. How does CYCLE impact the performance of the sequence?

• The performance impact of using CYCLE is minimal. However, in high-volume systems where sequence values are frequently accessed, it’s important to ensure the cycle is managed correctly, as wrapping around too quickly may lead to undesirable behavior or logical errors.

12. What is a practical use case for CYCLE?

• A common use case for CYCLE is for applications that require repeating number sequences, such as task allocation, round-robin scheduling, or generating repetitive codes. For example, assigning a fixed set of IDs to different groups repeatedly.

13. Can I use CYCLE to generate a sequence that goes back to a non-zero starting value?

• Yes, when CYCLE is enabled, the sequence will restart from the START WITH value after hitting the MAXVALUE or MINVALUE. The sequence will not necessarily go back to zero unless you specify it as the START WITH value.

14. How can I view the current value of a sequence with CYCLE enabled?

• You can use the CURRVAL to view the current value of the sequence. However, when using CYCLE, be mindful that the value could reset once the sequence exceeds its MAXVALUE or MINVALUE.

15. Does CYCLE work with CACHE or NO CACHE options in a sequence?

• Yes, the CYCLE option works in conjunction with CACHE or NO CACHE. If you choose to cache sequence values, it will cache the values until they are needed, regardless of whether CYCLE is enabled.