Practise · Preview, then delete

Opening your saved work…

The reading

Preview, then delete

SELECT COUNT(*) AS orders_left, MIN(order_date) AS earliest
FROM orders;

The question to ask after the delete: how many are left, and where does the data now start? Open in the playground

DELETE FROM orders WHERE order_date < '2026-01-20' removes whole rows, 71 of them. The same two rules apply: preview with the same WHERE first, and read what remains. 204 orders minus 71 is 133, and SELECT COUNT(*), MIN(order_date) FROM orders afterwards should say 133 and 2026-01-20. If it says 122, your boundary ate the 20th.

DELETE with no WHERE empties the table, row by row, with no undo in the browser and no undo on the desktop either, unless you were inside a transaction. The disposable copy means you can try it once to see what 'no rows' looks like.

Rule of thumb. Preview the rows, delete them, then count and inspect what remains.

Going deeper (optional, not on the exam)

With foreign keys on, a parent row with children refuses to go: DELETE FROM employees WHERE id = 24 fails with FOREIGN KEY constraint failed, because seven orders point at that employee. The database is protecting the orders. What to do about them is a design decision, which chapter 6 and Lab 10 cover.

Preview, then delete · DELETE ... WHERE, and what remains · level 6 of 6

Retire a piece of gear

Level 6: Transfer it · Exercise 1 of 1

Same idea as Preview, then delete, new data.

Trail Gear retires TG-102. Remove it from items by serial, then look at what remains.

Data: Trail Gear: build rehearsal. Every run starts from a fresh copy, so nothing you try here is permanent.

I would like help with this exercise

Each run starts from a fresh copy of the data, then shows the rows the question is about.

Table & column names only · ↑ ↓ choose · Tab insert · Esc dismiss

Open in the playground

Query results

Run to see the rows the question is about.

Practice here is evidence for you and your instructor, never a grade. Grades live in Canvas.