MySQL是目前使用最廣泛的關系型數據庫管理系統。它支持多種查詢方式，其中子查詢是常用的一種。MySQL中的子查詢可以嵌套在SELECT語句、FROM語句、WHERE語句、HAVING語句和INSERT語句中，用于返回一些需要用到的值或數據。

根據子查詢嵌套的位置，MySQL的子查詢可以分為以下幾種類型：

1. 標量子查詢
SELECT name, age, (SELECT MAX(salary) FROM employee e2 WHERE e1.department_id=e2.department_id) AS max_salary
FROM employee e1;
2. 行子查詢
SELECT * FROM employee WHERE department_id IN (SELECT department_id FROM department WHERE name='IT');
3. 列子查詢
SELECT name, age, (SELECT salary FROM salary_history WHERE employee_id=e.id ORDER BY date DESC LIMIT 1) AS current_salary
FROM employee e;
4. 子查詢作為表
SELECT e.*
FROM (SELECT * FROM employee WHERE department_id=1) e
JOIN department d ON e.department_id=d.id;
5. EXISTS子查詢
SELECT *
FROM employee e
WHERE EXISTS (SELECT * FROM salary_history WHERE employee_id=e.id AND salary>10000);
6. ANY/SOME子查詢
SELECT *
FROM employee
WHERE salary >ANY (SELECT salary FROM manager WHERE department_id=1);
7. ALL子查詢
SELECT *
FROM employee
WHERE salary >ALL (SELECT salary FROM manager WHERE department_id=1);

以上就是MySQL中常用的七種子查詢類型。使用這些子查詢可以大大增加查詢的靈活性，幫助開發者更加高效地完成數據管理。當然，在實際的開發過程中，若使用不當會導致性能問題，應該根據具體的業務場景選擇最合適的子查詢類型。