LEFT JOIN

SQL LEFT JOIN Keyword

The LEFT JOIN command is used to return all rows from the left table, and the matched rows from the right table. If there is no match, the result is NULL from the right side.

SQL LEFT JOIN Syntax

SELECT column_names
FROM table1
LEFT JOIN table2
ON table1.column_name = table2.column_name;

SQL LEFT JOIN Patients and Appointments Example

This query returns all patients, including those who may not have any appointments. If no match is found in the Appointments table, the related columns return NULL.

SELECT Patients.first_name, Appointments.appointment_id
FROM Patients
LEFT JOIN Appointments ON Patients.patient_id = Appointments.patient_id;

SQL LEFT JOIN Prescriptions and Appointments Example

This query shows all appointments and their corresponding prescriptions (if any). Appointments without a prescription will still be shown.

SELECT Appointments.appointment_id, Prescriptions.prescription_id
FROM Appointments
LEFT JOIN Prescriptions ON Appointments.appointment_id = Prescriptions.appointment_id;

SQL LEFT JOIN Labs