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Auto-increment allows a unique number to be generated automatically when a new record is inserted into a table
Auto-increment allows a unique number to be generated automatically when a new record is inserted into a table.
Often this is the primary key field that we would like to be created automatically every time a new record is inserted.
The following SQL statement defines the "Personid" column to be an auto-increment primary key field in the "Persons" table:
CREATE TABLE Persons
(
Personid int NOT NULL AUTO_INCREMENT,
LastName varchar(255) NOT NULL,
FirstName varchar(255),
Age int,
PRIMARY KEY (Personid)
);
MySQL uses the AUTO_INCREMENT
keyword to perform an auto-increment feature.
By default, the starting value for AUTO_INCREMENT
is 1, and it will increment by 1 for each new record.
To let the AUTO_INCREMENT
sequence start with another value, use the following SQL statement:
ALTER TABLE Persons AUTO_INCREMENT=100;
To 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 statement above would insert a new record into the "Persons" table. The "Personid" column would be assigned a unique value. The "FirstName" column would be set to "Lars" and the "LastName" column would be set to "Monsen".
The following SQL statement defines the "Personid" column to be an auto-increment primary key field in the "Persons" table:
CREATE TABLE Persons
(
Personid int IDENTITY(1,1) PRIMARY KEY,
LastName varchar(255) NOT NULL,
FirstName varchar(255),
Age int
);
The MS SQL Server uses the IDENTITY
keyword to perform an auto-increment feature.
In the example above, the starting value for
IDENTITY
is 1, and it will increment by 1 for each new record.
IDENTITY(10,5)
.
To 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 statement above would insert a new record into the "Persons" table. The "Personid" column would be assigned a unique value. The "FirstName" column would be set to "Lars" and the "LastName" column would be set to "Monsen".
The following SQL statement defines the "Personid" column to be an auto-increment primary key field in the "Persons" table:
CREATE TABLE Persons
(
Personid AUTOINCREMENT PRIMARY KEY,
LastName varchar(255) NOT NULL,
FirstName varchar(255),
Age int
);
The MS Access uses the AUTOINCREMENT
keyword to perform an auto-increment feature.
By default, the starting value for AUTOINCREMENT
is 1, and it will increment by 1 for each new record.
AUTOINCREMENT(10,5)
.
To 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 statement above would insert a new record into the "Persons" table. The "Personid" column would be assigned a unique value. The "FirstName" column would be set to "Lars" and the "LastName" column would be set to "Monsen".
In Oracle the code is a little bit more tricky.
You will have to create an auto-increment field with the sequence object (this object generates a number sequence).
Use the following CREATE SEQUENCE
syntax:
CREATE SEQUENCE seq_person
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.
To 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):
INSERT INTO Persons (Personid,FirstName,LastName)
VALUES (seq_person.nextval,'Lars','Monsen');
The SQL statement above would insert a new record into the "Persons" table. The "Personid" column would be assigned the next number from the seq_person sequence. The "FirstName" column would be set to "Lars" and the "LastName" column would be set to "Monsen".