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What is COMMIT?

COMMIT saves all changes made during a transaction. Once you COMMIT, the changes are permanent and cannot be undone.

Think of COMMIT like clicking the Save button after editing a document. Before you save, you can still undo your changes. After you save, the changes are final.

How COMMIT Works

Basic Syntax

BEGIN;

-- Make your changes
UPDATE table SET column = value WHERE condition;
INSERT INTO table (columns) VALUES (values);

COMMIT;  -- All changes are now permanent

What Happens When You COMMIT

Before COMMIT:

Your changes exist only in your session
Other users cannot see your changes
The database can still undo everything
Changes are in a temporary state

After COMMIT:

Changes are written to permanent storage
All other users can now see the changes
The changes survive server restarts
You cannot undo with ROLLBACK anymore

Real-life Example: Updating User Profile

A user wants to update their profile information. They change their name, email, and phone number.

BEGIN;

UPDATE users SET name = 'John Smith' WHERE user_id = 1;
UPDATE users SET email = 'john.smith@email.com' WHERE user_id = 1;
UPDATE users SET phone = '555-1234' WHERE user_id = 1;

-- All changes look good, save them
COMMIT;

After COMMIT, the user profile is updated permanently.

Real-life Example: Processing Payment

When a customer pays for an order, several things must happen and be saved together.

BEGIN;

-- Record the payment
INSERT INTO payments (order_id, amount, status) VALUES (1001, 99.99, 'completed');

-- Update order status
UPDATE orders SET status = 'paid', paid_at = NOW() WHERE order_id = 1001;

-- Update customer purchase history
UPDATE customers SET total_purchases = total_purchases + 99.99 WHERE customer_id = 5;

COMMIT;  -- Payment is now officially recorded

COMMIT vs ROLLBACK

You have two choices at the end of a transaction:

COMMIT - Save all changes permanently

Use when everything worked correctly
Changes become visible to everyone
Cannot be undone

ROLLBACK - Cancel all changes

Use when something went wrong
All changes are discarded
Database returns to state before BEGIN

BEGIN;

UPDATE accounts SET balance = balance - 500 WHERE user_id = 1;
UPDATE accounts SET balance = balance + 500 WHERE user_id = 2;

-- If transfer is correct:
COMMIT;

-- If something is wrong:
-- ROLLBACK;

When to COMMIT

COMMIT when:

All operations completed successfully
Data has been verified
You are ready to make changes permanent

Do not COMMIT when:

An error occurred during the transaction
You are not sure the data is correct
You might need to undo the changes

Summary

COMMIT makes your transaction permanent:

All changes are saved to the database
Other users can now see the changes
The changes survive crashes and restarts
You cannot undo after COMMIT

Always verify your changes before running COMMIT.