Sequences

Sequences can be used to set the default values of columns to sequential integer values. Sequences guarantee uniqueness, and help avoid constraint enforcement problems and overhead. Sequences are especially useful for primary key columns.

While sequence object values are guaranteed to be unique, they are not guaranteed to be contiguous. For example, two nodes can increment a sequence at different rates. The node with a heavier processing load increments the sequence, but the values are not contiguous with those being incremented on a node with less processing. For details, see Distributing sequences.

Vertica supports the following sequence types:

• Named sequences are database objects that generates unique numbers in sequential ascending or descending order. Named sequences are defined independently through CREATE SEQUENCE statements, and are managed independently of the tables that reference them. A table can set the default values of one or more columns to named sequences.
• IDENTITY column sequences increment or decrement column's value as new rows are added. Unlike named sequences, IDENTITY sequence types are defined in a table's DDL, so they do not persist independently of that table. A table can contain only one IDENTITY column.