Try this problem in the playground
The sample tables will be auto-loaded — write a query and run it instantly.
Find gaps in sequential data
Given order IDs 1, 2, 3, 5, 6, 8, 9 — identify the missing IDs (4 and 7). Useful for finding deleted records or audit gaps.
Setup & sample data
The playground will create these tables and populate them automatically when you click "Open Playground" above:
Solutions
Multiple approaches — try each and understand the trade-offs.