mysql中exist的用法

SELECT column_name(s)
FROM table_name
WHERE EXISTS (subquery);

SELECT *
FROM customers
WHERE EXISTS (SELECT 1 FROM orders WHERE customers.customer_id = orders.customer_id);

SELECT *
FROM products
WHERE price > 100 AND EXISTS (SELECT 1 FROM stock WHERE products.product_id = stock.product_id AND stock.quantity > 0);

CREATE TABLE customers (
    customer_id INT PRIMARY KEY,
    name VARCHAR(100)
);

CREATE TABLE orders (
    order_id INT PRIMARY KEY,
    customer_id INT,
    order_date DATE
);

SELECT *
FROM customers
WHERE EXISTS (SELECT 1 FROM orders WHERE customers.customer_id = orders.customer_id);