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#0356
Prevent Join Duplicate Explosion
MediumSQL24 min20 XP
Problem
Return user_id, orders_count, and tickets_count without multiplying rows between orders and tickets.
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, user_id INTEGER); tickets(ticket_id INTEGER, user_id INTEGER)
Examples
Example 1
Inputuser 1 has 2 orders and 3 tickets
Output2 and 3, not 6
Pre-aggregation avoids order-ticket row multiplication.
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
Inputuser 1 has 2 orders and 3 tickets
Expected[[1,2,3],[2,1,1]]
Pre-aggregation avoids order-ticket row multiplication.
Hidden Test Categories
Empty or missing matchesDuplicate rows or tiesNULL values where the pattern commonly breaks