SQL AUTO INCREMENT Field
SQL AUTO INCREMENT Field
An auto-increment field is a numeric column that automatically generates a unique number, when a new record is inserted into a table.
The auto-increment field is typically the
PRIMARY KEY field that we want to
automatically be assigned a unique number, every time a new record is inserted.
Syntax for MySQL
MySQL uses the AUTO_INCREMENT 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),
Age int
);
The default starting value for AUTO_INCREMENT is 1, and it will increment by 1 for each new record.
To let AUTO_INCREMENT start with another value, use the following SQL statement:
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):
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.
Syntax for SQL Server
The SQL Server uses the IDENTITY 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),
Age int
);
In the example above, the starting value for
IDENTITY is 1, and it will increment by 1 for each new record.
Tip: 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):
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.
Syntax for MS Access
The MS Access uses the AUTOINCREMENT 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),
Age int
);
The default starting value for AUTOINCREMENT is 1, and it will increment by 1 for each new record.
Tip: 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):
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.
Syntax for Oracle
In Oracle, you have to create an auto-increment field with the
SEQUENCE object (this object generates a number sequence).
Here is the CREATE SEQUENCE syntax:
MINVALUE 1
START WITH 1
INCREMENT BY 1
CACHE 10;
The code above creates a SEQUENCE object called seq_person, that starts with 1 and will increment by 1.
It will also cache up to 10 values for performance. The cache option specifies how many sequence values will be stored in memory for faster access.
When we insert a new record into the "Persons" table, we will have to use the nextval function (this function retrieves the next value from seq_person sequence):
VALUES (seq_person.nextval, 'Lars', 'Monsen');
The SQL above inserts a new record into the "Persons" table, and the "Personid" column would be assigned the next unique number from the seq_person sequence.