Back to Practice
#0344

Union All Event Volume

EasySQL15 min10 XP

Problem

Return the total number of event rows across 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(event_id INTEGER); app_events(event_id INTEGER)

Examples

Example 1
Input2 web rows and 3 app rows
Output5

UNION ALL keeps every row, including duplicate event_id values.

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
Input2 web rows and 3 app rows
Expected[[5]]

UNION ALL keeps every row, including duplicate event_id values.

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