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#0339
Cohort Size by Signup Month
EasySQL15 min10 XP
Problem
Return cohort_month and users_count ordered by cohort_month.
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
users(user_id INTEGER, signup_date TEXT)
Examples
Example 1
Inputtwo January signups
OutputJanuary cohort size 2
A cohort is usually defined by signup month.
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 January signups
Expected[["2026-01",2],["2026-02",1]]
A cohort is usually defined by signup month.
Hidden Test Categories
Empty or missing matchesDuplicate rows or tiesNULL values where the pattern commonly breaks