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#0345
Users Active on Web and App
EasySQL15 min10 XP
Problem
Return user_id values that appear in both web_events and app_events.
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
web_events(user_id INTEGER); app_events(user_id INTEGER)
Examples
Example 1
Inputusers 2 and 3 appear in both
Output2, 3
INTERSECT keeps only values present in both queries.
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
Inputusers 2 and 3 appear in both
Expected[[2],[3]]
INTERSECT keeps only values present in both queries.
Hidden Test Categories
Empty or missing matchesDuplicate rows or tiesNULL values where the pattern commonly breaks