About
A sequence is a auxiliary relational data structure that maintains a sequence.
Relational sequences are generally used to create a generated primary key via an incremental number.
Transparency usage
They may also be used transparently when a auto-increment instruction in SQL is given on a column
For example with SQlite:
CREATE TABLE foo (
id INT autoincrement,
description TEXT
);
Query
Database may give you the possibility to query the actual or next value of a sequence.
Example with an Oracle sequence.
select my_sequence.nextval from dual;
Database implementation
- IDENTITY in SQL Server
- SEQUENCE/NEXTVAL in Oracle
- AUTOINCREMENT in Access, SQlite
Number to text and id protection
- https://hashids.org/php - YouTube-like ids from numbers with a salt to protect the id