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Overview
An auto-increment field is a numeric column that automatically generates a unique number, when a new record is inserted into a table.
Formula
The auto - increment field is typically the PRIMARY KEYfield that we want to automatically be assigned a unique number, every time a new record is inserted.
AUTO_INCREMENT
Formula
keyword to perform an auto - increment feature.
The following SQL defines the "Personid" column to be an auto - increment primary key field in the "Persons" table:( Personid int AUTO_INCREMENT PRIMARY KEY, LastName varchar(255) NOT NULL, FirstName varchar(255),
);AUTO_INCREMENT is 1, and it will increment by 1 for each new record.
AUTO_INCREMENT start with another value, use the following SQL statement:
ALTER TABLE Persons AUTO_INCREMENT = 100;
When we insert a new record into the "Persons" table, we will NOT have to specify a value for the "Personid"
column (a unique value will be added automatically):
INSERT INTO Persons (FirstName, LastName)
VALUES ('Lars', 'Monsen');
The SQL above inserts a new record into the "Persons" table, and the
"Personid" column will automatically be assigned the next unique number.Formula
keyword to perform an auto - increment feature.
The following SQL defines the "Personid" column to be an auto - increment primary key field in the "Persons" table:( Personid int IDENTITY(1,1) PRIMARY KEY, LastName varchar(255) NOT NULL, FirstName varchar(255),
);In the example above, the starting value for
is 1, and it will increment by 1 for each new record.
To specify that the "Personid" column should start at value 10 and increment by 5, change it to IDENTITY(10,5). When we insert a new record into the "Persons" table, we will NOT have to specify a value for the "Personid" column (a unique value will be added automatically): INSERT INTO Persons (FirstName, LastName)
VALUES ('Lars', 'Monsen');
The SQL above inserts a new record into the "Persons" table, and the
"Personid" column will automatically be assigned the next unique number.Formula
keyword to perform an auto - increment feature.The following SQL statement defines the "Personid" column to be an auto-increment primary key field in the "Persons" table:
( Personid AUTOINCREMENT PRIMARY KEY, LastName varchar(255) NOT NULL, FirstName varchar(255),
);is 1, and it will increment by 1 for each new record.
To specify that the "Personid" column should start at value 10 and increment by 5, change the autoincrement to AUTOINCREMENT(10,5). When we insert a new record into the "Persons" table, we will NOT have to specify a value for the "Personid" column (a unique value will be added automatically): INSERT INTO Persons (FirstName, LastName)
VALUES ('Lars', 'Monsen');
The SQL above inserts a new record into the "Persons" table, and the
"Personid" column will automatically be assigned the next unique number.Formula
In Oracle, you have to create an auto - increment field with the SEQUENCEobject (this object generates a number sequence).
syntax: CREATE SEQUENCE seq_person