For a descending sequence, specify a value for the MINVALUE parameter. To create a sequence that stops at a predefined limit, for an ascending sequence, specify a value for the MAXVALUE parameter. For descending sequences, omit the MINVALUE parameter or specify the NOMINVALUE. To create a sequence that increments without bound, for ascending sequences, omit the MAXVALUE parameter or specify NOMAXVALUE. Specifying only INCREMENT BY -1 creates a descending sequence that starts with -1 and decreases with no lower limit. If you specify none of the following clauses, then you create an ascending sequence that starts with 1 and increases by 1 with no upper limit. Specify the name of the sequence to be created. If you omit schema, then Oracle Database creates the sequence in your own schema.
Specify the schema to contain the sequence. To create a sequence in another user's schema, you must have the CREATE ANY SEQUENCE system privilege.ĭescription of the illustration create_sequence.gif To create a sequence in your own schema, you must have the CREATE SEQUENCE system privilege. "How to Use Sequence Values " for information on using sequencesĪLTER SEQUENCE or DROP SEQUENCE for information on modifying or dropping a sequence
Once a sequence is created, you can access its values in SQL statements with the CURRVAL pseudocolumn, which returns the current value of the sequence, or the NEXTVAL pseudocolumn, which increments the sequence and returns the new value.Ĭhapter 3, " Pseudocolumns" for more information on using the CURRVAL and NEXTVAL Additionally, a single user may not realize that other users are drawing from the same sequence. It is possible that individual sequence numbers will appear to be skipped, because they were generated and used in a transaction that ultimately rolled back. Sequence numbers are generated independently of tables, so the same sequence can be used for one or for multiple tables. Once a sequence value is generated by one user, that user can continue to access that value regardless of whether the sequence is incremented by another user. One user can never acquire the sequence number generated by another user. If two users concurrently increment the same sequence, then the sequence numbers each user acquires may have gaps, because sequence numbers are being generated by the other user. When a sequence number is generated, the sequence is incremented, independent of the transaction committing or rolling back. You can use sequences to automatically generate primary key values. Use the CREATE SEQUENCE statement to create a sequence, which is a database object from which multiple users may generate unique integers.
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