SQL Dialects Reference/Data structure definition/Auto-increment column

A short hint: In most cases auto-increment columns are used as Primary Key columns. In the SQL standard the junction of the two concepts is not mandatory.

SQL Standard
The SQL standard defines two ways to generate auto-increment values. First, there are identity columns as an extension to exact numeric types. The syntax is: "GENERATED { ALWAYS | BY DEFAULT } AS IDENTITY". Second, the use of sequences in combination with triggers is standardized.

DB2
Identity columns or sequences combined with triggers (comparison of both techniques).

Firebird
Is recommended to use sequences combined with triggers. From 3.0 there is Identity support.

Linter
AUTOINC columns (maybe with RANGEs) or sequences combined with triggers.

SQLite
Both create an autoincrementing column; the AUTOINCREMENT keyword only prevents reusing deleted values.