57. Chain of Doctors

Hard Self Join

Query Rules

The query columns and order must match the expected result schema.
NULL values should be handled appropriately where applicable.
The grader compares output values and sorting order to evaluate.

Schema Browser

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patients

10 cols

patient_id

INTEGER

first_name

VARCHAR(30)

last_name

VARCHAR(30)

gender

CHAR(1)

birth_date

DATE

city

VARCHAR(30)

province_id

CHAR(2)

allergies

VARCHAR(80)

height

DECIMAL(3,0)

weight

DECIMAL(4,0)

doctors

4 cols

admissions

7 cols

province_names

2 cols

Reference Solution

Expected SQL

SELECT d1.last_name, d2.last_name, d3.last_name FROM doctors d1 JOIN doctors d2 ON d1.specialty = d2.specialty JOIN doctors d3 ON d2.first_name = d3.first_name WHERE d1.doctor_id != d2.doctor_id AND d2.doctor_id != d3.doctor_id;

SQL Editor

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Console Output

Console Terminal

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