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Hospital Triage: Elevated Systolic Blood Pressure

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 retrieve all patient vital readings from `triage_vitals` where `systolic_bp >= 140`. Include a computed column named `hypertension_stage`: - If `systolic_bp >= 180`, classify as `'CRISIS'` - Otherwise, classify as `'STAGE_2'` Return: 1. `patient_id` 2. `systolic_bp` 3. `diastolic_bp` 4. `hypertension_stage` Order results by `systolic_bp` descending, then by `patient_id` ascending.

Why Technical Interviewers Ask This

Emergency triage clinical systems continuously evaluate vitals recorded at triage check-in to classify hypertension severity for attending nursing staff.

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 
        patient_id,
        systolic_bp,
        diastolic_bp,
        CASE 
          WHEN systolic_bp >= 180 THEN 'CRISIS'
          ELSE 'STAGE_2'
        END AS hypertension_stage
      FROM triage_vitals
      WHERE systolic_bp >= 140
      ORDER BY systolic_bp DESC, patient_id ASC;

Approach Breakdown

This query addresses the problem requirements by filtering and structuring data in Fundamentals. It meets the target criteria: Patient triage records with elevated systolic readings classified by crisis urgency.

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.