sql中decode的用法

DECODE(expression, value1, result1, value2, result2, ..., default_result)

SELECT DECODE(name, NULL, 'Unknown', name) FROM customers;

SELECT DECODE(age, NULL, 0, age) FROM employees;

SELECT DECODE(gender, 'M', 'Male', 'F', 'Female', 'Other') FROM students;

CREATE TABLE sales (
  product_id INT,
  product_name VARCHAR(50),
  category VARCHAR(20),
  sales_amount DECIMAL(10, 2)
);

INSERT INTO sales (product_id, product_name, category, sales_amount) VALUES
(1, 'Smart TV', 'Electronics', 2000.00),
(2, 'iPhone', 'Electronics', 1500.00),
(3, 'Coffee Maker', 'Appliances', 300.00),
(4, 'Microwave', 'Appliances', 450.00);

SELECT
  product_name,
  category,
  DECODE(sales_amount,
    NULL, 'No Sales',
    2000.00, 'High Sales',
    1500.00, 'Medium Sales',
    'Low Sales') AS sales_category
FROM sales;

product_name | category | sales_category
Smart TV      | Electronics | High Sales
iPhone        | Electronics | Medium Sales
Coffee Maker  | Appliances | Low Sales
Microwave     | Appliances | Low Sales