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#0380
Preview Orphan Orders
MediumSQL24 min20 XP
Problem
Return order_id values whose customer_id does not exist in customers.
Why This Matters
SQL interviews usually test whether you can turn a business question into the right rows, grouping level, join type, and edge-case behavior.
Schema
orders(order_id INTEGER, customer_id INTEGER); customers(customer_id INTEGER)
Examples
Example 1
Inputorder 11 references customer 3
Outputorder 11
A missing dimension match becomes NULL after the LEFT JOIN.
Constraints
- Return only the requested columns.
- Use deterministic ORDER BY when multiple rows are returned.
- Assume SQLite-compatible SQL unless the prompt states otherwise.
CodeSQL
Visible browser tests run here when available.
Testcases1 visible / 3 hidden categories
Core SQL case
Inputorder 11 references customer 3
Expected[[11]]
A missing dimension match becomes NULL after the LEFT JOIN.
Hidden Test Categories
Empty or missing matchesDuplicate rows or tiesNULL values where the pattern commonly breaks