Oracle SQL Experts: INCREMENT BY FAQS

1. What does the INCREMENT BY clause do in Oracle sequences?

The INCREMENT BY clause defines the step size by which the sequence will be incremented (or decremented) each time NEXTVAL is called. It controls how much the sequence number increases or decreases.

2. What is the default value for INCREMENT BY?

If the INCREMENT BY clause is not specified, Oracle defaults the increment to 1. This means the sequence will generate values like 1, 2, 3, 4, ....

3. Can I specify a negative value for INCREMENT BY?

Yes, you can specify a negative value for INCREMENT BY, which creates a descending sequence. For example:

CREATE SEQUENCE seq_example

START WITH 100

INCREMENT BY -5;

This will generate values like 100, 95, 90, 85, 80, and so on.

4. What happens if I use INCREMENT BY 0?

If you set INCREMENT BY 0, the sequence will not increment and will always return the same value every time NEXTVAL is called. This is generally not a common use case because the sequence will not produce a series of unique numbers.

5. Can I change the INCREMENT BY value of an existing sequence?

No, once a sequence is created, you cannot directly change the INCREMENT BY value. You would need to drop the sequence and recreate it with the desired increment value.

6. What happens when the sequence reaches the MAXVALUE or MINVALUE with INCREMENT BY?

If a sequence has reached its MAXVALUE (for ascending sequences) or MINVALUE (for descending sequences), and CYCLE is enabled, the sequence will restart from its START WITH value (or MINVALUE for descending sequences). If NOCYCLE is specified, the sequence will raise an error once the limit is reached.

7. How does the INCREMENT BY value interact with the CYCLE option?

If you use the CYCLE option, the sequence will continue to generate values, even after reaching the MAXVALUE or MINVALUE. For example, with an ascending sequence starting at 1 and an increment of 1, once it hits the MAXVALUE, it will restart at the START WITH value (or MINVALUE in descending sequences).

8. What is the difference between INCREMENT BY 1 and INCREMENT BY -1?

INCREMENT BY 1 will produce an ascending sequence, starting from the START WITH value and increasing by 1 each time.
INCREMENT BY -1 will produce a descending sequence, starting from the START WITH value and decreasing by 1 each time.

9. Can INCREMENT BY be used with START WITH in both ascending and descending sequences?

10. How do I know the next value of a sequence with a non-default increment?

You can retrieve the next value of the sequence by calling NEXTVAL. The sequence will return the next value based on the current value and the specified increment. For example, if the sequence starts at 100 and increments by 5, the first call to NEXTVAL will return 100, the second will return 105, and so on.

11. Can I specify a very large value for INCREMENT BY?

Yes, you can specify a large INCREMENT BY value as long as it fits within the bounds of the data type used for the sequence. However, very large values may lead to overflow issues, so you should be cautious when specifying extremely large increments.

12. What happens if I specify an INCREMENT BY value larger than MAXVALUE or smaller than MINVALUE?

If the INCREMENT BY value would cause the sequence to exceed the defined MAXVALUE or MINVALUE, Oracle will raise an error when you attempt to create or alter the sequence.

13. How does INCREMENT BY work with the NOCYCLE option?

If you specify NOCYCLE, once the sequence reaches the MAXVALUE (for ascending sequences) or MINVALUE (for descending sequences), it will stop generating values, and the next call to NEXTVAL will result in an error.

14. Can INCREMENT BY be used in combination with START WITH and MAXVALUE?

Yes, you can specify both START WITH and MAXVALUE along with INCREMENT BY. The sequence will start at the specified START WITH value, increment by the specified INCREMENT BY value, and stop at or before the MAXVALUE.

Oracle SQL Experts