Changing rows with UPDATE

UPDATE changes values in the rows that match a WHERE condition:

UPDATE product SET price = 0.95 WHERE code = 'P02';

SET lists the columns to change. You can change several at once, separated by commas: SET price = 0.95, in_stock = 150.

UPDATE with a WHERE changes only the matching row's cell

Always use WHERE

The WHERE decides which rows change. Leave it out and every row is updated:

UPDATE product SET price = 0;   -- changes ALL products!

So nearly every UPDATE should have a WHERE. The checker runs your UPDATE, then reads the table back to confirm only the right row changed.

Common mistakes

UPDATE without a WHERE changes every row — always add the WHERE.
Set several columns at once with commas.

Change the price of the product with code 'P02' to 0.95. Be sure to use a WHERE so only that product changes.

UPDATE product SET price = ... WHERE code = 'P02';

Click Run to see the output here.

A delivery arrived, so every product gains 10 in stock. Update with an expression — SET in_stock = in_stock + 10 — and no WHERE, so it applies to all rows.

UPDATE product SET in_stock = ...;

Click Run to see the output here.

Updating rows

Changing rows with UPDATE

Always use WHERE

Common mistakes

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