Write carefully
Reading data can't hurt. Changing it can: an UPDATE without WHERE changes *every* row. Learn the three commands — and the habit of checking what you'll change before you change it.
INSERT, UPDATE, DELETE
INSERT INTO dishes (name, category, price, veg)
VALUES ('Yomari', 'Snack', 90, true), ('Chatamari', 'Snack', 150, false)
RETURNING id, name;
UPDATE dishes SET price = price + 10 WHERE category = 'Drink' RETURNING name, price;
SELECT name FROM dishes WHERE price > 400;
DELETE FROM dishes WHERE price > 400 AND name <> 'Thakali set' RETURNING name;
SELECT count(*) FROM dishes;- Deleting rows that others reference (foreign keys) fails — next lesson.
- "Upsert": INSERT … ON CONFLICT (name) DO UPDATE SET price = excluded.price (PostgreSQL course).