7、MySQL数据库-连接查询

七、连接查询

1.sql92

1.1 等值连接

1.查询女神名和对应的男神名
select NAME,boyName 
from boys,beauty 
where beauty.boyfriend_id = boys.id;

2.为表起别名-查询员工名、工作岗位号、工作岗位名
select e.last_name,e.job_id,job_title 
from employees e,jobs j 
where e.job_id=j.job_id;

3.两个表的顺序调换-查询员工名、岗位号、工种名
select e.last_name,e.job_id,job_title 
from jobs j,employees e 
where e.job_id=j.job_id;

4.加筛选-查询城市名中第二个字符为o的部门名和城市名
select department_name,city 
from departments d,location l 
where d.location_id = l.location_id 
and city like '_o%';

5.实现三表连接-查询员工名、部门名和所在的城市以S开头的
select last_name,department_name,city 
from employees e,departments d,location l 
where e.department_id=d.department_id and d.location_id=l.location_id and city like 's%';

1.2自连接

1.查询员工名和上级的名称
select e.employee_id,e.last_name,m.employee_id,last_name 
from employee e,employee m
where e.manager_id=m.manager_id;

2.sql99

2.1内连接-等值连接

1.查询员工名和部门名
SELECT last_name,department_name
FROM departments d,employees e  
WHERE e.department_id =d.department_id;

2.加筛选条件-（1）查询部门编号>100的部门名和所在的城市名
SELECT department_name,city
FROM departments d
JOIN locations l
ON d.`location_id` = l.`location_id`
WHERE d.`department_id`>100;

3.加筛选条件-（2）查询名字中包含E的员工名和工作岗位名
SELECT last_name,job_title
FROM employees e
JOIN jobs j
ON e.`job_id`=j.`job_id`
WHERE e.`last_name` LIKE '%e%';

4.添加分组+筛选-查询每个城市的部门个数
SELECT COUNT(*) 部门个数,l.`city`
FROM departments d
JOIN locations l
ON d.`location_id`=l.`location_id`
GROUP BY l.`city`;

5.添加分组+筛选+排序-查询每个部门中员工个数>10的部门名，并按员工个数降序
SELECT COUNT(*) 员工个数,d.department_name
FROM employees e
JOIN departments d
ON e.`department_id`=d.`department_id`
GROUP BY d.`department_id`
HAVING 员工个数>10
ORDER BY 员工个数 DESC;

6.添加多表查询-查询员工名、部门名、工作岗位名，并按部门名降序
SELECT last_name,department_name,job_title
FROM employees e
JOIN departments d ON e.`department_id`=d.`department_id`
JOIN jobs j ON e.`job_id`=j.`job_id`
ORDER BY department_name DESC;

2.2内连接-非等值连接

1.查询员工的工资级别
SELECT salary,grade_level
FROM employees e
JOIN job_grades g
ON e.`salary` BETWEEN g.`lowest_sal` AND g.`highest_sal`;

2.查询部门编号在10-90之间的员工的工资级别，并按级别进行分组
SELECT e.`salary`,g.`grade_level`,e.`department_id`
FROM employees e
JOIN job_grades g
ON e.`salary` BETWEEN g.`lowest_sal` AND g.`highest_sal`
WHERE e.`department_id` BETWEEN 10 AND 90
GROUP BY g.`grade_level`;

3.查询每个工资级别的个数>20的个数，并且按工资级别降序
SELECT COUNT(*),grade_level
FROM employees e
JOIN job_grades g
ON e.`salary` BETWEEN g.`lowest_sal` AND g.`highest_sal`
GROUP BY grade_level
HAVING COUNT(*)>20
ORDER BY grade_level DESC

2.3内连接-自连接

1.查询员工名和对应的领导名
SELECT e.`last_name`,m.`last_name`
FROM employees e
JOIN employees m
ON e.`manager_id`=m.`employee_id`;

2.查询姓名中含有字符K的员工名和对应的领导名
SELECT e.`last_name`,m.`last_name`
FROM employees e
JOIN employees m
ON e.`manager_id`=m.`employee_id`
WHERE e.last_name LIKE '%K%';