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Stop 1 of 5 · Ticket booth: two stamps, one receipt
Trick to keep in mind+3 XP
All or nothing: a failure takes its earlier statements down with it.
A transaction makes a group of statements atomic. If a later statement fails and the transaction is rolled back, the earlier ones in it are undone as well, not just the failing one. Without that, you would be left with half a change, such as an order recorded for tickets that were never taken out of stock.
Read it once, then a question tests whether the trick stuck.