Defining an Identity Column

An identity column is a column that stores numbers that increment by one with each insertion. Identity columns are sometimes called autoincrement columns. Derby provides autoincrement as a built-in feature; see CREATE TABLE statement in the Derby Reference Manual.

Below is an example that shows how to use an identity column to create the MAP_ID column of the MAPS table in the toursDB database.

CREATE TABLE MAPS
(
MAP_ID INTEGER NOT NULL GENERATED ALWAYS AS IDENTITY (START WITH 1, INCREMENT BY 1),
MAP_NAME VARCHAR(24) NOT NULL,
REGION VARCHAR(26),
AREA DECIMAL(8,4) NOT NULL,
PHOTO_FORMAT VARCHAR(26) NOT NULL,
PICTURE BLOB(102400),
UNIQUE (MAP_ID, MAP_NAME)
)