Test a lost update scenario

Reproduce two clerks overwriting each other's stock change, then fix it with atomic relative updates.

1. 1SAVEPOINT lost_update; both clerks read product 12's stock (500), e.g. into a TEMP table.
2. 2Clerk A writes 500 - 30 and clerk B writes 500 - 20 as absolute values; observe 480 instead of 450.
3. 3ROLLBACK TO lost_update and RELEASE it to undo the buggy run.
4. 4Apply both sales safely: UPDATE products SET stock = stock - 30 WHERE id = 12, then stock - 20.
5. 5Verify: SELECT id, stock FROM products WHERE id = 12 returns 450.

• Product 12 ends with stock 450
• The last result set is (12, 450)
• The fix uses a relative update (stock = stock - n)

• Every run starts from a freshly seeded database, so your script must include its own setup statements.
• The workbench has a single connection, so concurrent sessions are simulated step by step inside one session (snapshots in TEMP tables, SAVEPOINTs as the other transaction).
• Only the last result set of your script is compared, so finish with the verification query.