MySQL 자식 쿼리 클래식 사례
이 블로그에는 모든 유형의 하위 쿼리가 포함되어 있습니다. 읽은 후에는 다양한 유형의 하위 쿼리를 마스터 할 수 있습니다. 데이터베이스 파일이 필요한 경우 블로거에게주의를 기울이고 비공개 메시지로 가져 오세요.
1. 급여가 가장 낮은 사원의 정보를 질의합니다 : last_name, salary
#①查询最低的工资
SELECT MIN(salary)
FROM employees
#②查询last_name,salary,要求salary=①
SELECT last_name,salary
FROM employees
WHERE salary=(
SELECT MIN(salary)
FROM employees
);
2. 평균 급여가 가장 낮은 부서에 대한 정보 쿼리
#方式一:
#①各部门的平均工资
SELECT AVG(salary),department_id
FROM employees
GROUP BY department_id
#②查询①结果上的最低平均工资
SELECT MIN(ag)
FROM (
SELECT AVG(salary) ag,department_id
FROM employees
GROUP BY department_id
) ag_dep
#③查询哪个部门的平均工资=②
SELECT AVG(salary),department_id
FROM employees
GROUP BY department_id
HAVING AVG(salary)=(
SELECT MIN(ag)
FROM (
SELECT AVG(salary) ag,department_id
FROM employees
GROUP BY department_id
) ag_dep
);
#④查询部门信息
SELECT d.*
FROM departments d
WHERE d.`department_id`=(
SELECT department_id
FROM employees
GROUP BY department_id
HAVING AVG(salary)=(
SELECT MIN(ag)
FROM (
SELECT AVG(salary) ag,department_id
FROM employees
GROUP BY department_id
) ag_dep
)
);
#方式二:
#①各部门的平均工资
SELECT AVG(salary),department_id
FROM employees
GROUP BY department_id
#②求出最低平均工资的部门编号
SELECT department_id
FROM employees
GROUP BY department_id
ORDER BY AVG(salary)
LIMIT 1;
#③查询部门信息
SELECT *
FROM departments
WHERE department_id=(
SELECT department_id
FROM employees
GROUP BY department_id
ORDER BY AVG(salary)
LIMIT 1
);
3. 평균 급여가 가장 낮은 부서의 정보와 부서의 평균 급여를 조회합니다.
#①各部门的平均工资
SELECT AVG(salary),department_id
FROM employees
GROUP BY department_id
#②求出最低平均工资的部门编号
SELECT AVG(salary),department_id
FROM employees
GROUP BY department_id
ORDER BY AVG(salary)
LIMIT 1;
#③查询部门信息
SELECT d.*,ag
FROM departments d
JOIN (
SELECT AVG(salary) ag,department_id
FROM employees
GROUP BY department_id
ORDER BY AVG(salary)
LIMIT 1
) ag_dep
ON d.`department_id`=ag_dep.department_id;
4. 평균 급여가 가장 높은 작업 정보를 쿼리합니다.
#①查询最高的job的平均工资
SELECT AVG(salary),job_id
FROM employees
GROUP BY job_id
ORDER BY AVG(salary) DESC
LIMIT 1
#②查询job信息
SELECT *
FROM jobs
WHERE job_id=(
SELECT job_id
FROM employees
GROUP BY job_id
ORDER BY AVG(salary) DESC
LIMIT 1
);
5. 회사의 평균 급여보다 평균 급여가 높은 부서는 어디입니까?
#①查询平均工资
SELECT AVG(salary)
FROM employees
#②查询每个部门的平均工资
SELECT AVG(salary),department_id
FROM employees
GROUP BY department_id
#③筛选②结果集,满足平均工资>①
SELECT AVG(salary),department_id
FROM employees
GROUP BY department_id
HAVING AVG(salary)>(
SELECT AVG(salary)
FROM employees
);
6. 회사의 모든 관리자에 대한 세부 정보를 질의합니다.
#①查询所有manager的员工编号
SELECT DISTINCT manager_id
FROM employees
#②查询详细信息,满足employee_id=①
SELECT *
FROM employees
WHERE employee_id =ANY(
SELECT DISTINCT manager_id
FROM employees
);
7. 각 부서에서 가장 낮은 급여를받는 부서의 최저 임금은 얼마입니까?
#①查询各部门的最高工资中最低的部门编号
SELECT department_id
FROM employees
GROUP BY department_id
ORDER BY MAX(salary)
LIMIT 1
#②查询①结果的那个部门的最低工资
SELECT MIN(salary) ,department_id
FROM employees
WHERE department_id=(
SELECT department_id
FROM employees
GROUP BY department_id
ORDER BY MAX(salary)
LIMIT 1
);
8. 평균 연봉이 가장 높은 부서장의 상세 정보 조회 : last_name, department_id, email, salary
#①查询平均工资最高的部门编号
SELECT
department_id
FROM
employees
GROUP BY department_id
ORDER BY AVG(salary) DESC
LIMIT 1
#②将employees和departments连接查询,筛选条件是①
SELECT
last_name, d.department_id, email, salary
FROM
employees e
INNER JOIN departments d
ON d.manager_id = e.employee_id
WHERE d.department_id =
(SELECT
department_id
FROM
employees
GROUP BY department_id
ORDER BY AVG(salary) DESC
LIMIT 1) ;