EasyFundamentals

Customer Loyalty Tier Classification with CASE WHEN

Frequently Asked By:AppleGoogleAmazon

Interactive In-Browser Workspace

Practice this problem on live schema tables in PostgreSQL 16 WASM with instant row verification and visual EXPLAIN plans.

Solve in Workbench

Problem Statement

Write a query to assign each customer in `loyalty_members` a loyalty tier based on `lifetime_spend`: - `>= 5000.00` -> `'Platinum'` - `>= 2000.00` -> `'Gold'` - `>= 500.00` -> `'Silver'` - Else -> `'Bronze'` Alias the generated column as `tier_name`. Return: 1. `member_id` 2. `first_name` 3. `last_name` 4. `lifetime_spend` 5. `tier_name` Order results by `lifetime_spend` descending, then by `member_id` ascending.

Why Technical Interviewers Ask This

LuxeApparel is launching a VIP reward program. Marketing wants a segmented view of customer accounts categorizing their spend into loyalty tiers: 'Platinum' for $5,000+, 'Gold' for $2,000 - $4,999.99, 'Silver' for $500 - $1,999.99, and 'Bronze' for below $500.

Common Pitfalls & Interview Traps

Forgetting required sorting and deterministic tie-breaking.

Not accounting for NULL or zero-value denominators during calculations.

Using inefficient quadratic subqueries instead of single-pass fundamentals constructs.

Canonical Modern SQL Solution

PostgreSQL 16 / ANSI SQL

SELECT 
        member_id,
        first_name,
        last_name,
        lifetime_spend,
        CASE 
          WHEN lifetime_spend >= 5000.00 THEN 'Platinum'
          WHEN lifetime_spend >= 2000.00 THEN 'Gold'
          WHEN lifetime_spend >= 500.00 THEN 'Silver'
          ELSE 'Bronze'
        END AS tier_name
      FROM loyalty_members
      ORDER BY lifetime_spend DESC, member_id ASC;

Approach Breakdown

This query addresses the problem requirements by filtering and structuring data in Fundamentals. It meets the target criteria: Customer profiles with computed loyalty tier labels sorted by lifetime spend.

Edge Cases to Verbally Clarify with Your Interviewer

The dataset contains zero matching records (must return valid empty result without crashing).

Multiple records tie on sorting criteria (must evaluate tie-breaking order deterministically).

Foreign keys or secondary attributes have NULL values.

Frequently Asked Follow-Up Questions

What makes this question a favorite among Apple and Google interviewers?

Interviewers use this problem to test whether candidates write defensive, scalable Fundamentals queries that run efficiently on multi-million row production databases without excessive memory usage.

How does the query optimizer execute this query?

Using single-pass table scans with index lookups or sort buffers. Running EXPLAIN (ANALYZE, BUFFERS) in the DB Exercises workbench visualizes the execution nodes and buffer hit cache.