MySQL复合查询深度解析

SELECT 列名
FROM 表1
INNER JOIN 表2 ON 表1.列 = 表2.列;

SELECT e.name, d.dept_name
FROM employees e
INNER JOIN departments d ON e.dept_id = d.dept_id;

SELECT e.name, d.dept_name, p.project_name
FROM employees e
INNER JOIN departments d ON e.dept_id = d.dept_id
INNER JOIN projects p ON e.project_id = p.id;

SELECT 列名
FROM 左表
LEFT [OUTER] JOIN 右表
ON 左表.列 = 右表.列;

SELECT e.name, d.dept_name
FROM employees e
LEFT JOIN departments d ON e.dept_id = d.dept_id;

SELECT 列列表
FROM 左表
RIGHT [OUTER] JOIN 右表
ON 连接条件;

SELECT s.id, st.name, s.score
FROM students st
RIGHT JOIN scores s ON st.id = s.student_id;

SELECT 列
FROM 表名 AS A
JOIN 表名 AS B ON A.某列 = B.某列
[WHERE / GROUP BY / ...];

SELECT  e.name   AS employee,
        m.name   AS manager
FROM    employees AS e
LEFT JOIN employees AS m
       ON e.manager_id = m.emp_id;

SELECT ...
FROM 表1
WHERE 列 运算符 (SELECT 单列
                 FROM 表2
                 WHERE 条件
                 LIMIT 1);   -- 确保只返回一行

SELECT name, salary
FROM   employees
WHERE  salary > (SELECT AVG(salary) FROM employees);

SELECT stu_name
FROM   students
WHERE  stu_id IN (SELECT stu_id FROM enroll WHERE course = '数学');

SELECT name
FROM   employees
WHERE  salary > ANY (SELECT salary FROM employees WHERE dept_id = 10);

SELECT name
FROM   employees
WHERE  salary > ALL (SELECT salary FROM employees WHERE dept_id = 10);

SELECT name
FROM   students s
WHERE  EXISTS (SELECT 1
               FROM   scores sc
               WHERE  sc.stu_id = s.stu_id
               AND    sc.score > 90);

SELECT name
FROM   employees
WHERE  (dept_id, job_title) IN (
        SELECT dept_id, job_title
        FROM   employees
        WHERE  name = '张三'
);

SELECT d.dept_name, t.avg_sal
FROM (
        SELECT dept_id, AVG(salary) AS avg_sal
        FROM   emp
        GROUP  BY dept_id
     ) AS t
JOIN dept d ON d.dept_id = t.dept_id
WHERE t.avg_sal > 8000;

SELECT name FROM employees
UNION
SELECT name FROM contractors;

SELECT name FROM employees
UNION ALL
SELECT name FROM contractors;