);
案例2：返回 job_id与141好员工相同，salary比143号员工多的员工 姓名，job_id和工资
#①查询141号员工的job_id
SELECT job_id
FROM employees
WHERE employee_id=141;
#②查询143号员工的salary
SELECT salary
FROM employees
WHERE employee_id=143
#查询员工的姓名,job_id和工资，要求job_id=①并且salary>②
SELECT last_name,job_id,salary
FROM employees
WHERE job_id=(
SELECT job_id
FROM employees
WHERE employee_id=141
) AND salary>(
SELECT salary
FROM employees
WHERE employee_id=143
);
案例3：返回工资最少的员工的last_name,job_id和salary
#①查询工资的最低工资
SELECT MIN(salary)
FROM employees
#②查询last_name,job_id,salary,要求salary=①
SELECT last_name,job_id,salary
FROM employees
WHERE salary=(
SELECT MIN(salary)
FROM employees
);
案例4：查询最低工资大于50号部门最低工资的部门id和其最低工资
#①查询50号部门的最低工资
SELECT MIN(salary)
FROM employees
WHERE department_id=50
#②查询每个部门的最低工资
SELECT MIN(salary),department_id
FROM employees
GROUP BY department_id
#③在②基础上筛选，满足min(salary)>①
SELECT MIN(salary),department_id
FROM employees
GROUP BY depart 《一线大厂Java面试题解析+后端开发学习笔记+最新架构讲解视频+实战项目源码讲义》无偿开源 威信搜索公众号【编程进阶路】 ment_id
HAVING MIN(salary)>(
SELECT MIN(salary)
FROM employees
WHERE department_id=50
);
#非法使用标量子查询
SELECT MIN(salary),department_id
FROM employees
GROUP BY department_id
HAVING MIN(salary)>(
SELECT salary
FROM employees
WHERE department_id=50
);
#单行操作符只能搭配单行子查询
[](()2、列子查询(多行子查询)
_返回多行
使用多行比较操作符_
**操作符 含义
IN/NOT IN 返回列表中的任意一个
ANY|some 和子查询返回的某一个值比较 <可以用MIN替换>
ALL 和子查询返回的所以值比较 <可以用MAX替换>**
案例1：返回location_id是1400或1700的部门中所以员工姓名
#①查询location_id是1400或1700的部门编号
SELECT department_id
FROM departments
WHERE location_id IN(1400,1700);
#②查询员工姓名，要求部门号是①列表中的某一个
SELECT last_name
FROM employees
WHERE department_id IN(
SELECT department_id
FROM departments
WHERE location_id IN(1400,1700)
);
案例2：返回其他工种中比job_id为’IT_PROG’部门任一工资低的员工的员工号、姓名、job_id以及salary
#①查询job_i为’IT_PROG’部门任意工资
SELECT salary
FROM employees
WHERE job_id=‘IT_PROG’
#②查询员工号、姓名、job_id以及salary,salary<①的任意一个
#法1
SELECT last_name,employee_id,job_id,salary
FROM employees
WHERE salary<ANY(
SELECT salary
FROM employees
WHERE job_id=‘IT_PROG’
)AND job_id<>‘IT_PROG’;
#法2
SELECT last_name,employee_id,job_id,salary
FROM employees
WHERE salary<(
SELECT MAX(salary)
FROM employees
WHERE job_id=‘IT_PROG’
)AND job_id<>‘IT_PROG’;
[](()3、行子查询(结果集一行多列或多行多列)
案例：查询员工编号最小并且工资最高的员工信息
#①查询最小的员工编号
SELECT MIN(employee_id)
FROM employees
#②查询最高工资
SELECT MAX(salary)
FROM employees
#③查询员工信息
SELECT *
FROM employees
WHERE employee_id=(
SELECT MIN(employee_id)
FROM employees
)AND salary=(
SELECT MAX(salary)
FROM employees
);
#法2
SELECT *
FROM employees
WHERE (employee_id,salary)=(
SELECT MIN(employee_id),MAX(salary)
FROM employees
);
[](()(二)、select后面
仅仅支持标量子查询
案例1：查询每个部门的员工个数
SELECT d.*,(
SELECT COUNT(*)
FROM employees e
WHERE e.department_id=d.department_id
)
FROM departments d;
案例2：查询员工号=102的部门名
SELECT (
SELECT department_name
FROM departments d
INNER JOIN employees e
ON d.department_id=e.department_id
WHERE e.employee_id=102
) 部门名;
[](()(三)、from后面
_**特点：
将子查询的结果充当一张表，要求必须起别名**_
案例：查询每个部门的平均工资的工资等级
#①查询每个部门的平均工资
SELECT AVG(salary),department_id
FROM departments
GROUP BY department_id
#②连接①的结果集和job_grades表，筛选条件平均工资between lowest_sal and highest_sal
SELECT ag_dep.*,g.grade_level
FROM (
SELECT AVG(salary) ag,department_id
FROM employees
GROUP BY department_id
) ag_dep
INNER JOIN job_grades g
ON ag_dep.ag BETWEEN lowest_sal AND highest_sal;
[](()(四)、exists后面(相关子查询)
_**语法:
exists(完整的查询语句)
结果：
1<存在>或0<不存在>**_
SELECT EXISTS(SELECT employee_id FROM employees);
案例1：查询有员工的部门名
SELECT department_name
FROM departments d
WHERE EXISTS(
SELECT *
FROM employees e
WHERE d.department_id=e.department_id
);
