Database Testing / Quiz
JOINs for the Prosecution
INNER drops, LEFT keeps, and a fan-out silently doubles your totals. SQL joins as a validation weapon, not just a query tool.
- Difficulty
- Easy
- Format
- Quiz
- Points
- 100
- Estimate
- 10 min
// MISSION BRIEF
Your Mission
A tester who can JOIN can interrogate any dataset. This quiz covers join semantics through a validation lens: finding orphans with anti-joins, catching fan-out row multiplication, and the count tricks that expose bad data.
Scoring: timed quiz; accuracy first, speed bonus for fast clean runs.
// FIRST CONTACT
Battle teaser
`orders INNER JOIN customers ON customers.id = orders.customer_id` returns:
- AAll orders, with NULL customers where unmatched
- BAll customers, even those without orders
- CThe cartesian product of both tables
- DOnly rows with a match on both sides; orders with no matching customer silently vanish from the result
Answers, scoring, hints, and the full battle stay sealed.
// SKILL TAGS
sqldatabase-testingjoinsdata-validation