Examples of the usage of sequences in SQL

Editor to share with you an example of the use of sequences in SQL, I believe most people do not know much about it, so share this article for your reference, I hope you can learn a lot after reading this article, let's go to know it!

1. Grammar

Create sequence dept_deptno

Increment by 1

Start with 91

Maxvalue 100

Nocache

Nocycle

Increment by n: step size, how much does it increase each time? default is 1.

Start with n: initial value, default 1

Maximum value of maxvalue ascending sequence. There is no maximum by default.

Minimum value of minvalue descending sequence. There is no minimum by default.

Cycle: after reaching the maximum value, there is a loop. Cycle cannot be used in primary key columns. Default nocycle. The initial beginning after the loop starts at 1, no matter how the original value is set.

Cache: how much is cached. Default is 20. To improve performance, oracle sends out sequence values in batches in advance and caches them so that they can be sent to users.

2. Pseudo column

Nextval: next sequence value

Select dept_deptno.nextval from dual

Currval: current sequence value. The first access is to have no current sequence value.

Select dept_deptno.currval from dual

3. View

USER_SEQUENCE

4. Modify and delete

ALTER (syntax is similar to create statement)

DROP

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