一篇文章彻底弄懂MySQL的多种连接方式

SELECT 
      Person.lastName,Person.firstName,Address.city,Address.state
FROM 
      Person
LEFT JOIN 
      Address 
ON 
      Person.personId = Address.personId;
 

-- 创建示例表
CREATE TABLE colors (
    color_name VARCHAR(20)
);

CREATE TABLE sizes (
    size_name VARCHAR(20)
);

-- 交叉连接：生成所有颜色和尺寸的组合
SELECT c.color_name, s.size_name
FROM colors c
CROSS JOIN sizes s;

-- 假设两个表都有相同的列名 id 和 name
SELECT *
FROM table1
NATURAL JOIN table2;

-- 连接三个表：订单、客户、产品
SELECT o.order_id, c.customer_name, p.product_name, o.quantity
FROM orders o
JOIN customers c ON o.customer_id = c.customer_id
JOIN products p ON o.product_id = p.product_id;

SELECT 列名
FROM 表1
JOIN 表2 USING (共同列名);

-- 使用 USING 替代 ON
SELECT e.name, d.name
FROM employees e
JOIN departments d USING (department_id);

-- 创建工资等级表
CREATE TABLE salary_grades (
    grade VARCHAR(10),
    min_salary INT,
    max_salary INT
);

-- 不等值连接：确定每个员工的工资等级
SELECT e.name, e.salary, sg.grade
FROM employees e
JOIN salary_grades sg ON e.salary BETWEEN sg.min_salary AND sg.max_salary;

-- 使用自连接
SELECT DISTINCT l1.num AS ConsecutiveNums
FROM  Logs l1
join Logs l2 on l1.id = l2.id -1 AND l1.num = l2.num
join Logs l3 on l1.id = l3.id -2 AND l1.num = l3.num

SELECT a.name AS Employee
FROM Employee a,Employee b
WHERE a.managerId = b.id
AND a.salary > b.salary

SELECT b.id
FROM Weather a,Weather b
WHERE a.Temperature < b.Temperature AND DATEDIFF (a.RecordDate,b.RecordDate) = -1

SELECT d.name as Department,e1.name as Employee,e1.salary AS Salary
FROM Employee e1
join Department d on  e1.departmentId = d.id
WHERE 3 >(
    SELECT count(DISTINCT e2.Salary)
    FROM Employee e2
    WHERE e2.salary > e1.salary
    AND e1.departmentId =  e2.departmentId
)

SELECT distinct s1.*
FROM Stadium s1, Stadium s2, Stadium s3
where(
    (s1.id = s2.id-1 AND s1.id = s3.id-2) or
    (s1.id = s2.id-1 AND s1.id = s3.id+1) or
    (s1.id = s2.id+1 AND s1.id = s3.id+2 )
)
AND s1.people >= 100
AND s2.people >= 100
AND s3.people >= 100
ORDER BY s1.visit_date;