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#0373
Find Missing Dates From Calendar
MediumSQL24 min20 XP
Problem
Return calendar days that have no matching sales row.
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
calendar(day TEXT); sales(day TEXT, revenue INTEGER)
Examples
Example 1
Inputsales are missing Jan 2
Output2026-01-02
The calendar table supplies dates that may be absent from sales.
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
Inputsales are missing Jan 2
Expected[["2026-01-02"]]
The calendar table supplies dates that may be absent from sales.
Hidden Test Categories
Empty or missing matchesDuplicate rows or tiesNULL values where the pattern commonly breaks