目录
文章内容如下
✏️前言
✏️一、where子句中使用子查询
SELECT name, age
FROM students
WHERE age > (SELECT AVG(age) FROM students);✏️二、from子句中使用子查询：
SELECT t1.name, t2.total_sales
FROM employees AS t1
INNER JOIN (SELECT employee_id, SUM(sales) AS total_sales FROM sales GROUP BY employee_id) AS t2
ON t1.id = t2.employee_id;✏️三、select子句中使用子查询
SELECT name, (SELECT COUNT(*) FROM orders WHERE customer_id = customers.id) AS order_count
FROM customers;✏️四、having子句中使用子查询
SELECT salesperson, SUM(amount) AS total_sales
FROM sales
GROUP BY salesperson
HAVING SUM(amount) > (SELECT AVG(amount) FROM sales);✏️五、exists和not exists运算符
SELECT column_name(s)
FROM table_name
WHERE EXISTS (SELECT column_name FROM table_name WHERE condition);✏️总结
通过在这些位置使用子查询，可以实现复杂的查询逻辑，并根据外部查询的结果生成动态数据。子查询是MySQL中非常有用的功能之一，可以提供更强大和灵活的数据处理能力；子查询真的真的是MySQL中强大且灵活的工具，可以帮助我们进行更复杂的数据分析和处理操作。
