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#0357

Deduplicate Events Keep First

MediumSQL24 min20 XP

Problem

For duplicate events by user_id and event_name, return the earliest event_id.

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_name TEXT, event_time TEXT)

Examples

Example 1
Inputtwo click events for user 1
Outputearliest click only

ROW_NUMBER ranks duplicates by event_time.

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
Inputtwo click events for user 1
Expected[[2,1,"click"],[3,1,"view"]]

ROW_NUMBER ranks duplicates by event_time.

Hidden Test Categories
Empty or missing matchesDuplicate rows or tiesNULL values where the pattern commonly breaks