SERIAL(n) data type

The SERIAL data type stores a sequential integer, of the INT data type, that is automatically assigned by the database server when a new row is inserted.

The default serial starting number is 1, but you can assign an initial value, n, when you create or alter the table.
  • You must specify a positive number for the starting number.
  • If you specify zero (0) for the starting number, the value that is used is the maximum positive value that already exists in the SERIAL column + 1.

The maximum value for SERIAL is 2,147,483,647. If you assign a number greater than 2,147,483,647, you receive a syntax error. Use the SERIAL8 or BIGSERIAL data type, rather than SERIAL, if you need a larger range.

A table can have no more than one SERIAL column, but it can have a SERIAL column and either a SERIAL8 column or a BIGSERIAL column.

SERIAL values in a column are not automatically unique. You must apply a unique index or primary key constraint to this column to prevent duplicate serial numbers. If you use the interactive schema editor in DB-Access to define the table, a unique index is applied automatically to a SERIAL column.

SERIAL numbers might not be consecutive, because of concurrent users, rollbacks, and other factors.

The DEFINE variable LIKE column syntax of SPL for indirect typing declares a variable of the INTEGER data type if column is a SERIAL data type.

After a number is assigned, it cannot be changed. You can insert a value into a SERIAL column (using the INSERT statement) or reset a serial column (using the ALTER TABLE statement), if the new value does not duplicate any existing value in the column. To insert into a SERIAL column, your database server increments by one the previous value (or the reset value, if that is larger) and assigns the result as the entered value. If ALTER TABLE has reset the next value of a SERIAL column to a value smaller than values already in that column, however, the next value follows this formula: 
(maximum existing value in SERIAL column) + 1
For example, if you reset the serial value of customer.customer_num to 50, when the largest existing value is 128, the next assigned number will be 129. For more details on SERIAL data entry, see the Informix® Guide to SQL: Syntax.

A SERIAL column can store unique codes such as order, invoice, or customer numbers. SERIAL data values require four bytes of storage, and have the same precision as the INTEGER data type. For details of another way to assign unique whole numbers to each row of a database table, see the CREATE SEQUENCE statement in Informix® Guide to SQL: Syntax.