How to alter sequence start value in Oracle?

Introduction

In Oracle, sequences are objects that generate unique numbers. Sometimes, you may need to alter the start value of a sequence to customize the numbering scheme for your application. In this article, we will explore how to alter the sequence start value in Oracle.

Altering Sequence Start Value

To alter the start value of a sequence in Oracle, you can use the ALTER SEQUENCE statement. Here is the syntax:

“`
ALTER SEQUENCE sequence_name RESTART WITH new_start_value;
“`

Replace `sequence_name` with the name of the sequence you want to modify and `new_start_value` with the new starting value for the sequence.

For example, if you want to set the start value of a sequence called `my_seq` to 1000, you can execute the following SQL statement:

“`
ALTER SEQUENCE my_seq RESTART WITH 1000;
“`

This will reset the sequence `my_seq` to start generating numbers from 1000 onwards.

Frequently Asked Questions

1. Can I alter the start value of a sequence without restarting it?

No, in Oracle, you need to restart the sequence in order to alter its start value.

2. What happens to the current sequence value when I alter the start value?

When you alter the start value of a sequence in Oracle, the current sequence value will not change. The new start value will only affect future sequence numbers generated.

3. Is it possible to alter the increment value of a sequence?

Yes, you can alter the increment value of a sequence in Oracle using the `INCREMENT BY` clause in the `ALTER SEQUENCE` statement.

4. Can I alter multiple sequences at once?

Yes, you can alter multiple sequences at once by executing multiple `ALTER SEQUENCE` statements in a single SQL script.

5. Is it necessary to have special privileges to alter a sequence start value?

You need `ALTER` privilege on the sequence to alter its start value in Oracle.

6. Can I alter the start value of a sequence in a transaction?

Yes, you can modify the start value of a sequence within a transaction in Oracle. The alteration will take effect for subsequent numbers generated within the same transaction.

7. Will altering the start value of a sequence impact existing data?

No, altering the start value of a sequence will not affect any existing data in your database. It only changes the starting point for future sequence numbers.

8. How can I view the current start value of a sequence?

You can query the `START WITH` clause of the sequence using the following SQL statement:

“`
SELECT start_with FROM user_sequences WHERE sequence_name = ‘my_seq’;
“`

Replace `my_seq` with the name of the sequence you want to check.

9. Can I alter the start value of a sequence to a value lower than the current sequence value?

Yes, you can set the start value of a sequence to a value lower than the current sequence value. However, the next number generated will still be greater than the current value.

10. Is it possible to alter the start value of a sequence to a negative number?

Yes, you can set the start value of a sequence to a negative number in Oracle. The sequence will continue to generate numbers starting from this negative value onwards.

11. How does altering the start value of a sequence impact performance?

Altering the start value of a sequence has negligible impact on performance. It is a quick operation that only changes the initial number generated by the sequence.

12. Can I alter the start value of a system-generated sequence?

No, you cannot alter the start value of a system-generated sequence in Oracle. System-generated sequences are managed by the database and their start values cannot be modified.

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