Auto Increment is used to automatically generate unique values for a column, usually a primary key, so that each record can be identified easily without manual input.It is useful when we need to:
- Maintain data consistency across different SQL databases.
- Support databases like SQL Server, MySQL, PostgreSQL, MS Access and Oracle.
1. SQL Server Auto Increment
In SQL Server, the Auto Increment feature is implemented using the IDENTITY property, which automatically generates unique values for new records.
- starting_value: The value from which numbering begins (e.g., 101).
- increment_value: The amount by which the value increases for each new record (e.g., 1).
Example
Create a Students table with Student_ID as an auto-increment primary key starting from 101.
CREATE TABLE Students(
Student_ID int IDENTITY(101, 1) PRIMARY KEY,
First_Name varchar(255),
Last_Name varchar(255)
);
Inserting Data with Auto Increment
To insert a new record into students table, we will not specify the value of Student_ID as it will be added automatically.
INSERT INTO Students(First_Name, Last_Name )
VALUES ('Deeksha', 'Jain');
INSERT INTO Students(First_Name, Last_Name )
VALUES ('Kavisha', 'Parikh');
Output:
2. MySQL Auto Increment
In MySQL, the AUTO_INCREMENT keyword is used to set a column as Auto Increment. By default, the counter starts at 1 and increases by 1 for each new row inserted.
Example
Create a Students table with Student_ID as an auto-increment primary key, along with First_Name and Last_Name fields.
CREATE TABLE Students(
Student_ID int AUTO_INCREMENT PRIMARY KEY,
First_Name varchar(255),
Last_Name varchar(255)
);
Inserting Data with Auto Increment
To insert a new record, we do not specify Student_ID because it is generated automatically for each new row.
INSERT INTO Students(First_Name, Last_Name )
VALUES ('Anish', 'Jain');
INSERT INTO Students(First_Name, Last_Name )
VALUES ('Akshita', 'Sharma');
INSERT INTO Students(First_Name, Last_Name )
VALUES ('Shruti', 'Sogani');
Output:
Changing Auto Increment Start Value
To change the default starting value we can use ALTER TABLE command as follows:
ALTER TABLE Students AUTO_INCREMENT = new_value; Adjusting the Increment Interval
In MySQL, the AUTO_INCREMENT value increases by 1 by default, but the increment interval can be changed using the auto_increment_increment system variable.
SET @@auto_increment_increment = new_interval_value;3. PostgreSQL Auto Increment
In PostgreSQL, the SERIAL keyword is used for auto-incrementing a column. This is a shorthand for creating an integer column that automatically increments.
Example
Create a Students table with Student_ID, First_Name and Last_Name, where Student_ID is an auto-increment primary key.
CREATE TABLE Students(
Student_ID int SERIAL PRIMARY KEY,
First_Name varchar(255),
Last_Name varchar(255)
);
Inserting Data with Auto Increment
To insert a new record into students table, we will not specify the value of Student_ID as it will be added automatically.
INSERT INTO Students(First_Name, Last_Name )
VALUES ('Anish', 'Jain');
INSERT INTO Students(First_Name, Last_Name )
VALUES ('Akshita', 'Sharma');
INSERT INTO Students(First_Name, Last_Name )
VALUES ('Shruti', 'Sogani');
Output:
4. MS Access Auto Increment
In MS Access, the AUTOINCREMENT keyword is used to define a column that automatically generates unique numeric values. Like MySQL and SQL Server, the default value starts at 1 and increments by 1.
Example
Create a Students table with Student_ID as an auto-increment primary key, along with First_Name and Last_Name fields.
CREATE TABLE Students(
Student_ID int AUTOINCREMENT PRIMARY KEY,
First_Name varchar(255),
Last_Name varchar(255)
);
Inserting Data with Auto Increment
To insert a record, Student_ID is not specified because it is generated automatically and increases by 1 for each new record.
INSERT INTO Students(First_Name, Last_Name )
VALUES ('Anish', 'Jain');
INSERT INTO Students(First_Name, Last_Name )
VALUES ('Akshita', 'Sharma');
INSERT INTO Students(First_Name, Last_Name )
VALUES ('Shruti', 'Sogani');
Output:
Changing Auto Increment Starting Value
In MS Access, the starting value and increment value of an AutoNumber field can be customized using:
AUTOINCREMENT(starting_value, increment_value)where starting_value is the initial value and increment_value is the step size for subsequent records.
5. Oracle Auto Increment
In Oracle, auto-increment is implemented using a SEQUENCE object, which generates a series of unique numbers for primary key values.
Syntax
CREATE SEQUENCE sequence_name
MINVALUE 1
START WITH 1
INCREMENT BY 1
CACHE 10;
- START WITH 101: Begins the sequence from 101.
- INCREMENT BY 1: Increments the value by 1 for each new record.
Example
The following code creates a sequence seq_students starting at 101 and incrementing by 1.
CREATE SEQUENCE seq_students
MINVALUE 1
START WITH 101
INCREMENT BY 1
CACHE 20;
Inserting Data with Auto Increment
To insert a new record into the Students table, use the NEXTVAL function to get the next value from the seq_students sequence.
INSERT INTO Students(Student_ID, First_Name, Last_Name)
VALUES (seq_students.nextval, 'Deeksha', 'Jain');
INSERT INTO Students(Student_ID, First_Name, Last_Name)
VALUES (seq_students.nextval, 'Kavisha', 'Parikh');
Output:
