SQL Group By

The GROUP BY statement groups rows with common values into summary rows. It is typically used with aggregate functions like COUNT(), SUM(), AVG(), MIN(), and MAX().

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SQL Group By Syntax

SELECT column_name(s)
FROM table_name
WHERE condition
GROUP BY column_name(s)
ORDER BY column_name(s);

SQL Group By Example

Count patients by gender:

Using the Patients table, we can count how many patients belong to each gender.

SELECT gender, COUNT(patient_id) AS total_patients
FROM Patients
GROUP BY gender;

Count medical records per patient:

This retrieves the number of medical records associated with each patient.

SELECT patient_id, COUNT(record_id) AS total_records
FROM MedicalRecords
GROUP BY patient_id;

SQL GROUP BY with JOIN Example

Count appointments per doctor:

To analyze appointment counts for each doctor, we join the Appointments and Doctors tables:

SELECT Doctors.first_name || ' ' || Doctors.last_name AS doctor_name, COUNT(Appointments.appointment_id) AS total_appointments
FROM Appointments
LEFT JOIN Doctors ON Appointments.doctor_id = Doctors.doctor_id
GROUP BY doctor_name;

SQL Group By Visual Diagram

SQL Group By Labs

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