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#0332
Running Event Count
MediumSQL24 min20 XP
Problem
Return user_id, event_date, and running_events for each event.
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
events(event_id INTEGER, user_id INTEGER, event_date TEXT)
Examples
Example 1
Inputuser 1 has two events
Outputrunning count 1 then 2
The window frame counts rows from the start of the user partition to the current row.
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 two events
Expected[[1,"2026-01-01",1],[1,"2026-01-03",2],[2,"2026-01-02",1]]
The window frame counts rows from the start of the user partition to the current row.
Hidden Test Categories
Empty or missing matchesDuplicate rows or tiesNULL values where the pattern commonly breaks