mysql合并逗号分隔

CREATE TABLE students (
    id INT PRIMARY KEY,
    name VARCHAR(50),
    course VARCHAR(50)
);

INSERT INTO students (id, name, course) VALUES
(1, 'Alice', 'Math'),
(2, 'Bob', 'Science'),
(3, 'Charlie', 'History');

SELECT CONCAT(name, ' - ', course) AS student_info
FROM students;

CREATE TABLE orders (
    id INT PRIMARY KEY,
    customer_name VARCHAR(50),
    product VARCHAR(50)
);

INSERT INTO orders (id, customer_name, product) VALUES
(1, 'Alice', 'Laptop'),
(2, 'Alice', 'Phone'),
(3, 'Bob', 'Tablet');

SELECT customer_name, GROUP_CONCAT(product SEPARATOR ', ') AS products
FROM orders
GROUP BY customer_name;

SET SESSION group_concat_max_len = 1000000;

SELECT customer_name, GROUP_CONCAT(IFNULL(product, 'N/A') SEPARATOR ', ') AS products
FROM orders
GROUP BY customer_name;