40 Subqueries

SELECT *
FROM products
WHERE unit_price >
    (SELECT unit_price
    FROM products
    WHERE product_id = 3)
## 筛选价格比莴笋贵的物品

SELECT *
FROM employees
WHERE salary >
    (SELECT AVG(salary)
    FROM employees)
## 筛选员工工资比平均高的

41 The IN Operator

• 使用subqueries的syntax

SELECT *
FROM clients
WHERE client_id NOT IN
    (SELECT DISTINCT client_id
    FROM invoices)
## 找出没有开发票的客户