Using Subqueries in Snowflake SQL as table source! Inline view table! Derive table.
In this video tutorial, you'll learn how to leverage the power of subqueries as table sources in Snowflake SQL. Dive into the basics of subquery syntax, understand their role in enhancing query efficiency, and discover practical examples of using subqueries to streamline your data analysis workflows in Snowflake. Whether you're a beginner or an experienced SQL user, this guide will equip you with the knowledge to make the most out of subqueries in Snowflake.
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SQL Query:-
-- Using Subqueries as table source
-- Create patients table
CREATE OR REPLACE TABLE patients (
patient_id INT PRIMARY KEY,
patient_name VARCHAR(100),
date_of_birth DATE,
gender VARCHAR(10)
);
-- Insert sample data into patients table
INSERT INTO patients (patient_id, patient_name, date_of_birth, gender)
VALUES
(1, 'John Doe', '1985-05-15', 'Male'),
(2, 'Jane Smith', '1978-12-28', 'Female'),
(3, 'Bob Johnson', '1990-08-10', 'Male');
SELECT * FROM patients;
-- Create medical_records table
CREATE OR REPLACE TABLE medical_records (
record_id INT PRIMARY KEY,
patient_id INT,
visit_date DATE,
diagnosis VARCHAR(100)
);
-- Insert sample data into medical_records table
INSERT INTO medical_records (record_id, patient_id, visit_date, diagnosis)
VALUES
(1, 1, '2023-07-10', 'Flu'),
(2, 1, '2023-09-20', 'Hypertension'),
(3, 2, '2023-06-05', 'Diabetes'),
(4, 2, '2023-08-15', 'Asthma'),
(5, 3, '2023-07-30', 'High cholesterol'),
(6, 3, '2023-10-25', 'Arthritis');
SELECT * FROM medical_records;
--the logic that the latest diagnosis should appaer in the report
--Select latest diagnosis for each patient:
SELECT
patient_id, visit_date, diagnosis
FROM medical_records a WHERE visit_date = (SELECT MAX(visit_date) FROM medical_records b
WHERE a.patient_id = b.patient_id);
-- Using subquery to find the latest medical condition for each patient
SELECT p.patient_id, p.patient_name, p.gender, mr.diagnosis
FROM patients p
INNER JOIN (
SELECT
patient_id, visit_date, diagnosis
FROM medical_records a WHERE visit_date = (SELECT MAX(visit_date) FROM medical_records b
WHERE a.patient_id = b.patient_id
)
) mr ON p.patient_id = mr.patient_id;
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