How to Add an Identity to an Existing Column in SQLite

An identity column as a column added to an existing table in SQLite would probably be a crucial task while database restructuring or when implementing new features. The identity column is provided with a compulsory key with auto-incremented values, which makes the administration of data easier and also enhances database efficiency.

In this article, we will understand the process of configuring the Identity Column to an already existing table in SQLite. We’ll talk about the list of steps, and advantages resulting from identity column utilization, and try to give enough instructions to help developers easily add this feature to their SQLite databases

Understanding Identity Columns

Identity columns in SQLite automatically assign unique, auto-incrementing values to each row in a table, often serving as primary keys. Unlike SQL Server, SQLite doesn’t offer native identity column support. Developers typically implement this functionality using techniques like AUTOINCREMENT or row counting to ensure data integrity and efficient data management.

How to Add an Identity to An Existing Column in SQLite

To add an identity to an existing column in SQLite, developers can use ALTER TABLE with AUTOINCREMENT, create a temporary table, copy data, add an identity column, or update identity values based on row positions. We will explore the three approaches:

• Using ALTER TABLE with AUTOINCREMENT
• Create a Temporary Table with an Identity Column and Copy Data
• Using a Temporary Table and ALTER TABLE to Add Identity

Setting up an Environment

Different approaches to add identity to an existing column are:

Consider the following database products,

CREATE TABLE products(
id INTEGER PRIIMARY KEY,
name TEXT,
price REAL
);

Inserting the value in products table:

INSERT INTO products (name, price ) VALUES 
('Product A' , 25.99),
('Product B' , 39.99),
('Product C' , 19.99),
('Product D' , 49.99),
('Product E' , 9.99);

1. Using ALTER TABLE with AUTOINCREMENT

In this approach, we’ll utilize the ALTER TABLE statement along with the AUTOINCREMENT keyword to add an identity column to an existing table.

Syntax:

ALTER TABLE table_name
ADD COLUMN column_name INTEGER PRIMARY KEY AUTOINCREMENT;

Example: Adding an Identity Column to the “Products” Table in SQLite

ALTER TABLE products
ADD COLUMN row_id INTEGER PRIMARY KEY AUTOINCREMENT;

Output:

Create a Temporary Table with Identity Column and Copy Data (Output)

Explanation:

• The row_id column is added to the products table with auto-incrementing values.
• The AUTOINCREMENT keyword ensures that each new row inserted into the table will have a unique, auto-incremented value for the row_id column.

2. Create a Temporary Table with Identity Column and Copy Data

This approach involves creating a temporary table with an identity column, copying data from the original table, and then renaming the temporary table to replace the original one.

Syntax:

CREATE TEMPORARY TABLE temp_table_name AS
SELECT column1, column2, ..., NULL AS column_name FROM original_table;

ALTER TABLE temp_table_name
ADD COLUMN column_name INTEGER PRIMARY KEY AUTOINCREMENT;

INSERT INTO temp_table_name (column1, column2, ..., column_name)
SELECT column1, column2, ..., NULL FROM original_table;

DROP TABLE original_table;

ALTER TABLE temp_table_name RENAME TO original_table;

Example: Modifying the “Products” Table to Add an Identity Column Using Temporary Tables in SQLite

-- Step1: Create a temprary table with an identity column 
CREATE TEMPORARY TABLE temp_products AS
SELECT id, name, price, NULL AS row_id FROM products;  

-- Step2: Alter the temporary table to add an identity column named "row_id"
ALTER TABLE  temp_products 
ADD COLUMN  row_id  INTEGER PRIMARY KEY AUTOINCREMENT; 

-- Step3: Insert data from the original "products" table into the temporary table
INSERT INTO temp_products ( id,name,price,row_id) 
SELECT id, name, price, NULL FROM products;  

-- Step4: Drop the original "products" table:
DROP TABLE products;

-- Rename the temporary table to replace the original "products" table
 ALTER TABLE  temp_products RENAME TO products;

Output:

Create a Temporary Table with Identity Column and Copy Data (Output)

Explanation:

• A temporary table temp_products is created with the same schema as the original products table, including an identity column named row_id.
• Data from the original products table is copied into the temporary table.
• The original products table is dropped, and the temporary table is renamed to replace it.

3. Using a Temporary Table and ALTER TABLE to Add Identity

In this approach, we’ll create a temporary table, copy data from the original table, add an identity column using ALTER TABLE, and then copy the data back.

Syntax:

CREATE TEMPORARY TABLE temp_table_name AS
SELECT column1, column2, ..., NULL AS column_name FROM original_table;

ALTER TABLE temp_table_name
ADD COLUMN column_name INTEGER;

UPDATE temp_table_name
SET column_name = (SELECT COUNT(*) FROM original_table WHERE original_table.primary_key <= temp_table_name.primary_key);

ALTER TABLE temp_table_name
ADD PRIMARY KEY (column_name);

INSERT INTO temp_table_name (column1, column2, ..., column_name)
SELECT column1, column2, ..., column_name FROM original_table;

DROP TABLE original_table;

ALTER TABLE temp_table_name RENAME TO original_table;

Example: Modifying the “Products” Table to Add an Identity Column Using Temporary Tables and Row Counting in SQLite

CREATE TEMPORARY TABLE  temp_products  AS
SELECT id, name, price, NULL AS row_id FROM products ;

ALTER TABLE  temp_products 
ADD COLUMN row_id INTEGER;

UPDATE  temp_products 
SET row_id = (SELECT COUNT(*) FROM products WHERE products.id <=temp_products.id);

ALTER TABLE  temp_products 
ADD PRIMARY KEY (row_id);

INSERT INTO  temp_products  (id, name, price ,row_id)
SELECT id, name, price, row_id FROM products ;

DROP TABLE products;

ALTER TABLE temp_products  RENAME TO products;

Output:

Using a Temporary Table and ALTER TABLE to Add Identity(Output)

Explanation:

• A temporary table temp_products is created with the same schema as the original products table, including a nullable identity column named row_id.
• The identity values are updated based on the row position in the original products table.
• The temporary table is altered to set the identity column as the primary key.
• Data from the temporary table is copied into the original products table.
• The original products table is dropped, and the temporary table is renamed to replace it.

Conclusion

While adding an identity column to an existing table in SQLite is easy and takes just a few simple steps, it is imperative to pay close attention to data integrity. The procedure detailed in this article along with some care will help you to add an identity column to your SQLite database and improve the structure of your tables. Keep in mind to always take a backup of your database before making any structural changes and test your changes thoroughly to make sure they are in compliance with your requirements. Through a proper knowledge of SQLite functionalities and the appropriate SQL commands, you can skillfully maintain and optimize your database schema and data management workflows.