Modifying Data with UPDATE

The UPDATE command lets you change existing data in your table.

Update a Single Row

UPDATE users SET email = 'alice.smith@example.com' WHERE id = 1;

What this does:

• UPDATE users = tells MySQL to modify data in the users table
• SET email = 'alice.smith@example.com' = change the email field to this new value
• WHERE id = 1 = only update the row where id is 1

What is the WHERE clause? The WHERE clause tells MySQL which rows to update. It’s like saying “only change the data for rows that match this condition.” Always use a unique field like id in your WHERE clause to make sure you’re updating the right row.

Important: The WHERE clause is crucial. Without it, you would update ALL rows in the table.

Update Multiple Fields

You can update multiple fields at once:

UPDATE users SET username = 'alice_smith', email = 'a.smith@example.com' WHERE id = 1;

Check Your Changes

After running UPDATE commands, use SELECT * FROM users; to see your changes: