SQL Case

The SQL Case statement is a useful command that allows you to perform conditional logic in SQL queries. It works similarly to if-else statements in programming languages that enables you to return different values based on specified conditions.

SQL Case Syntax

SELECT column_name,
    CASE
        WHEN condition1 THEN result1
        WHEN condition2 THEN result2
        ...
        ELSE resultN
    END AS new_column_name
FROM table_name;

SELECT column_name,

    CASE

        WHEN condition1 THEN result1

        WHEN condition2 THEN result2

        ...

        ELSE resultN

    END AS new_column_name

FROM table_name;

SQL Case Categorizing Patients by Appointment Status Example

This query joins the Patients table and the Appointments table, categorizing patients as “Active,” “Inactive,” or “Unknown” based on the appointment status.

SELECT p.first_name, p.last_name,
    CASE
        WHEN a.status = 'Scheduled' THEN 'Active Patient'
        WHEN a.status = 'Completed' THEN 'Inactive Patient'
        ELSE 'Unknown Status'
    END AS patient_status
FROM Patients p
JOIN Appointments a ON p.patient_id = a.patient_id;

SELECT p.first_name, p.last_name,

    CASE

        WHEN a.status = 'Scheduled' THEN 'Active Patient'

        WHEN a.status = 'Completed' THEN 'Inactive Patient'

        ELSE 'Unknown Status'

    END AS patient_status

FROM Patients p

JOIN Appointments a ON p.patient_id = a.patient_id;

SQL Case Visual Diagram

SQL Case Labs