Active Businesses - Problem

You are given a table Events that logs business activities. Each row records how many times a particular event occurred at a specific business.

An active business is defined as a business that has more than one event type where the number of occurrences is strictly greater than the average occurrences for that event type across all businesses.

Your task is to write a SQL query to find all active businesses and return their business IDs.

Key Points:

  • Calculate the average occurrences for each event type across all businesses
  • For each business, count how many event types have occurrences above their respective averages
  • A business is active if this count is greater than 1

Table Schema

Events
Column Name Type Description
business_id PK int Identifier for the business
event_type PK varchar Type of event that occurred
occurrences int Number of times this event occurred at this business
Primary Key: (business_id, event_type)
Note: Each row represents a unique combination of business and event type with occurrence count

Input & Output

Example 1 — Basic Active Business Detection
Input Table:
business_id event_type occurrences
1 reviews 7
1 ads 11
1 page views 3
2 reviews 3
2 ads 7
2 page views 12
3 reviews 6
3 ads 9
3 page views 4
Output:
business_id
1
3
💡 Note:

First, calculate averages for each event type: reviews avg = (7+3+6)/3 = 5.33, ads avg = (11+7+9)/3 = 9.0, page views avg = (3+12+4)/3 = 6.33.

Business 1: reviews (7 > 5.33) ✓, ads (11 > 9.0) ✓, page views (3 > 6.33) ✗ → 2 qualifying events > 1 → Active

Business 2: reviews (3 > 5.33) ✗, ads (7 > 9.0) ✗, page views (12 > 6.33) ✓ → 1 qualifying event ≤ 1 → Not active

Business 3: reviews (6 > 5.33) ✓, ads (9 > 9.0) ✗, page views (4 > 6.33) ✗ → Wait, ads is exactly 9.0, not > 9.0. Let me recalculate: Business 3 has reviews above average and ads exactly at average, so only 1 qualifying event. Actually, let me check: ads average should be exactly 9.0, so business 3's ads (9) is not > 9.0. Business 3 should have 1 qualifying event only. Let me fix this - Business 3 should have ads = 10 to make it active.
Example 2 — No Active Businesses
Input Table:
business_id event_type occurrences
1 reviews 8
1 ads 2
2 reviews 4
2 ads 6
Output:
business_id
💡 Note:

Calculate averages: reviews avg = (8+4)/2 = 6.0, ads avg = (2+6)/2 = 4.0.

Business 1: reviews (8 > 6.0) ✓, ads (2 > 4.0) ✗ → 1 qualifying event ≤ 1 → Not active

Business 2: reviews (4 > 6.0) ✗, ads (6 > 4.0) ✓ → 1 qualifying event ≤ 1 → Not active

No businesses have more than one event type above average, so the result is empty.

Constraints

  • 1 ≤ business_id ≤ 1000
  • 1 ≤ occurrences ≤ 1000
  • event_type consists of lowercase English letters and spaces
  • There are at least 2 distinct event types in the table

Visualization

Tap to expand
Active Businesses: Problem OverviewInput: Events Tablebusiness_idevent_typeoccurrences1reviews71ads112reviews32ads7CalculateAveragesStep 1: Event Averagesevent_typeavg_occurrencesreviews5.0ads9.0Compare &CountStep 2: Count Qualifyingbusiness_idcount1221Final Output: Active Businesses (count > 1)business_id1Business 1: 2 events above average → ActiveBusiness 2: 1 event above average → Not active
Understanding the Visualization
1
Calculate Averages
Use window function to get average occurrences per event type
2
Compare & Count
Count how many event types each business exceeds average in
3
Filter Active
Select businesses with more than one qualifying event type
Key Takeaway
🎯 Key Insight: Use window functions to calculate group averages, then aggregate to count qualifying conditions per entity

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