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#0318
Customer Order Counts Including Zero
MediumSQL24 min20 XP
Problem
Return every customer name and their order_count, including customers with zero orders.
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
customers(customer_id INTEGER, name TEXT); orders(order_id INTEGER, customer_id INTEGER)
Examples
Example 1
InputCara has no orders
OutputCara -> 0
COUNT(o.order_id) ignores NULL joined rows, so unmatched customers get 0.
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
InputCara has no orders
Expected[["Asha",2],["Ben",1],["Cara",0]]
COUNT(o.order_id) ignores NULL joined rows, so unmatched customers get 0.
Hidden Test Categories
Empty or missing matchesDuplicate rows or tiesNULL values where the pattern commonly breaks