SQL Auto Increment

In SQL databases, a primary key is important for uniquely identifying records in a table. However, sometimes it is not practical to manually assign unique values for each record, especially when handling large datasets. To simplify this process, SQL databases offer an Auto Increment feature that automatically generates unique numerical values for a specified column.

This article provides an in-depth guide on how to use the Auto Increment feature across popular SQL databases such as SQL Server, MySQL, PostgreSQL, MS Access, and Oracle, with practical examples and use cases.

1. SQL Server Auto Increment

In SQL Server, the Auto Increment feature is implemented using the IDENTITY property. This property allows the database to automatically generate unique numbers for each new record in a table.

• starting_value - specifies where the numbering starts (in this case, 101).
  
• increment_value -determines how much the value will increase for each new record (here, it’s 1).

Example

We will create a Student table with fields Student_ID, First_Name, and Last_Name, we will auto-generate Student_ID by using auto-increment and will make it the Primary Key for the table. Let the starting value of IDENTITY be 101 and we will increment the auto-generated key by 1 for each new record.

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

We will create Students table with fields Student_ID, First_Name, Last_Name, we will auto generate Student_ID by using auto increment and will make it Primary Key for the table.

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 into students table, we will not specify the value of Student_ID as it will be added automatically and the first record will have key as 1 and key for every subsequent record will increase by 1.

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, we can also modify the interval at which the AUTO_INCREMENT value increases. By default, it increments by 1, but we can change it using the auto_increment_increment system variable.

To change the increment value (i.e., the step by which the value increments), we can set the auto_increment_increment variable and new_interval_value is the interval value we would like to use.

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

We will create Students table with fields Student_ID, First_Name, Last_Name, we will auto generate Student_ID by using auto increment and will make it Primary Key for the table.

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

We will create Students table with fields Student_ID, First_Name, Last_Name, we will auto generate Student_ID by using auto increment and will make it Primary Key for the table.

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 new record into students table, we will not specify the value of Student_ID as it will be added automatically and the first record will have key as 1 and key for every subsequent record will increase by 1.

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, to change the default starting value and increment value we can use Autonumber Settings in the Table Design view as follows:

AUTOINCREMENT(starting_value, increment_value) 

Here starting_value is the starting value we would like to use and increment_value is the value by which we would like to increment the key for the subsequent record.

5. Oracle Auto Increment

In Oracle, to use auto increment feature we have to make the auto-increment field with the sequence object which successively generates a number sequence. The sequence generates a series of numbers that can be used to auto-increment the primary key.

Syntax

CREATE SEQUENCE sequence_name
MINVALUE 1
START WITH 1
INCREMENT BY 1
CACHE 10;

Key Terms

• START WITH 101: Begins the sequence from 101.
  
• INCREMENT BY 1: Increments the value by 1 for each new record.

Example

The code below creates a sequence object called seq_students, that starts with 101 and can increment by 1. It'll also cache up to 20 values for performance.

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, we will have to use the nextval function that retrieves the next value from 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:

Conclusion

The Auto Increment feature simplifies the process of managing unique values for primary keys across different SQL databases. Whether we are working with SQL Server, MySQL, PostgreSQL, MS Access, or Oracle, implementing auto-incrementing columns can help maintain data integrity and streamline database management. This feature ensures that each new record gets a unique identifier, automatically incrementing based on the configuration specified during the table creation.