CASE

Handles IF/THEN logic. It is structured with at least one pair of WHEN and THEN statements. Every CASE statement must be concluded with the END keyword. The ELSE statement is optional, providing a way to capture values not explicitly specified in the WHEN and THEN statements.

Syntax

CASE
    WHEN <condition_1> THEN <value_1>
  [ WHEN <condition_2> THEN <value_2> ]
  [ ... ]
  [ ELSE <value_n> ]
END AS <column_name>

Examples

This example categorizes employee salaries using a CASE statement, presenting details with a dynamically assigned column named "SalaryCategory":

-- Create a sample table
CREATE TABLE Employee (
    EmployeeID INT,
    FirstName VARCHAR(50),
    LastName VARCHAR(50),
    Salary INT
);

-- Insert some sample data
INSERT INTO Employee VALUES (1, 'John', 'Doe', 50000);
INSERT INTO Employee VALUES (2, 'Jane', 'Smith', 60000);
INSERT INTO Employee VALUES (3, 'Bob', 'Johnson', 75000);
INSERT INTO Employee VALUES (4, 'Alice', 'Williams', 90000);

-- Add a new column 'SalaryCategory' using CASE statement
-- Categorize employees based on their salary
SELECT
    EmployeeID,
    FirstName,
    LastName,
    Salary,
    CASE
        WHEN Salary < 60000 THEN 'Low'
        WHEN Salary >= 60000 AND Salary < 80000 THEN 'Medium'
        WHEN Salary >= 80000 THEN 'High'
        ELSE 'Unknown'
    END AS SalaryCategory
FROM
    Employee;

┌──────────────────────────────────────────────────────────────────────────────────────────┐
│    employeeid   │     firstname    │     lastname     │      salary     │ salarycategory │
├─────────────────┼──────────────────┼──────────────────┼─────────────────┼────────────────┤
│               1 │ John             │ Doe              │           50000 │ Low            │
│               2 │ Jane             │ Smith            │           60000 │ Medium         │
│               4 │ Alice            │ Williams         │           90000 │ High           │
│               3 │ Bob              │ Johnson          │           75000 │ Medium         │
└──────────────────────────────────────────────────────────────────────────────────────────┘