sql里exists使用实例

1. 查询所有存在订单的客户信息

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

2. 查询存在未完成任务的员工信息

SELECT *
FROM employees
WHERE EXISTS (
  SELECT *
  FROM tasks
  WHERE employees.employee_id = tasks.employee_id
    AND tasks.status <> 'completed'
);

3. 查询存在评论的电影信息

SELECT *
FROM movies
WHERE EXISTS (
  SELECT *
  FROM reviews
  WHERE movies.movie_id = reviews.movie_id
);