> For the complete documentation index, see [llms.txt](https://eric-zhang-seattle.gitbook.io/mess-around/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://eric-zhang-seattle.gitbook.io/mess-around/traditional-db/overview/sharding-id-generator-overview/id_autoincrement_key.md).

# Auto-increment key

* [MySQL auto-increment primary key](#mysql-auto-increment-primary-key)
  * [Cons](#cons)

## MySQL auto-increment primary key

* Different ways to define automatic incremental primary key

```sql
-- MySQL
create table ‘test’ (
  ‘id’  int(16) NOT NULL AUTO_INCREMENT,
  ‘name’  char(10) DEFAULT NULL,
  PRIMARY KEY(‘id’) 
) ENGINE = InnoDB;

-- Oracle create sequence
create sequence test_seq increment by 1 start with 1;
insert into test(id, name) values(test_seq.nextval, ' An example ');
```

### Cons

* Not unique in distributed environments.