Unique Identifiers Made Easy: Primary Key Implementation in SQLite
During Table Creation:
This is the recommended approach. You define the Primary Key constraint while creating the table itself using the CREATE TABLE
statement. There are two ways to do this:
- Primary Key on a Single Column:
CREATE TABLE my_table (
id INTEGER PRIMARY KEY, /* id is the primary key */
name TEXT,
age INTEGER
);
In this example, the id
column is declared as an integer and also marked as the Primary Key.
- Primary Key on Multiple Columns (Composite Key):
CREATE TABLE my_table (
customer_id INTEGER,
order_id INTEGER,
PRIMARY KEY (customer_id, order_id) /* Primary key on both columns */
);
Here, both customer_id
and order_id
together form the Primary Key for the table. No two rows can have the same combination of values in these columns.
Important Points:
- SQLite doesn't allow adding a Primary Key to an existing table.
- If you need a Primary Key on an existing table, you'll have to create a new table with the desired Primary Key definition and then copy the data from the old table to the new one.
CREATE TABLE customers (
id INTEGER PRIMARY KEY, /* id is the primary key */
name TEXT NOT NULL,
age INTEGER
);
This code creates a table named customers
with three columns:
id
: An integer column set as the Primary Key, ensuring unique values for each customer.name
: A text column to store customer names.
Primary Key on Multiple Columns (Composite Key - During Table Creation):
CREATE TABLE orders (
customer_id INTEGER,
order_id INTEGER,
product_name TEXT,
quantity INTEGER,
PRIMARY KEY (customer_id, order_id) /* Primary key on both customer_id and order_id */
);
customer_id
: An integer column referencing a customer.order_id
: An integer column for order identification.product_name
: A text column to store the product name in the order.quantity
: An integer column for the quantity of the product ordered.
- Define a new table with the same structure as your existing table, but ensure it includes the desired Primary Key constraint during creation using
CREATE TABLE
.
Transfer Data from Existing Table:
- Use an
INSERT INTO
statement to copy all data from the old table to the new table.
(Optional) Drop the Old Table:
- Once the data transfer is complete and verified, you can optionally drop the old table if you no longer need it.
Here's an example to illustrate this process:
-- Existing table without Primary Key (assuming a table named 'products')
CREATE TABLE products (
name TEXT,
price REAL
);
-- New table with Primary Key on 'id' (assuming a new table named 'products_new')
CREATE TABLE products_new (
id INTEGER PRIMARY KEY AUTOINCREMENT, /* Auto-incrementing id as Primary Key */
name TEXT NOT NULL,
price REAL
);
-- Transfer data from old table to new table
INSERT INTO products_new (name, price)
SELECT name, price FROM products;
-- Optional: Drop the old table (after verifying data transfer)
DROP TABLE products;
Important Considerations:
- This approach requires creating a new table and copying data, so it might not be ideal for very large tables.
- Make sure to back up your data before performing these operations to avoid any potential issues.
- Foreign key constraints referencing the old table will need to be updated to point to the new table after the data transfer.
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