[SQL] New Companies

✅ New Companies

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📝 문제

Amber's conglomerate corporation just acquired some new companies. Each of the companies follows this hierarchy:

Given the table schemas below, write a query to print the company_code, founder name, total number of lead managers, total number of senior managers, total number of managers, and total number of employees. Order your output by ascending company_code.

Note

• The tables may contain duplicate records.
• The company_code is string, so the sorting should not be numeric. For example, if the company_codes are C_1, C_2, and C_10, then the ascending company_codes will be C_1, C_10, and C_2.

Input Format
The following tables contain company data:

• Company: The company_code is the code of the company and founder is the founder of the company.

• Lead_Manager: The lead_manager_code is the code of the lead manager, and the company_code is the code of the working company.

• Senior_Manager: The senior_manager_code is the code of the senior manager, the lead_manager_code is the code of its lead manager, and the company_code is the code of the working company.

• Manager: The manager_code is the code of the manager, the senior_manager_code is the code of its senior manager, the lead_manager_code is the code of its lead manager, and the company_code is the code of the working company.

• Employee: The employee_code is the code of the employee, the manager_code is the code of its manager, the senior_manager_code is the code of its senior manager, the lead_manager_code is the code of its lead manager, and the company_code is the code of the working company.

Sample Input
Company Table:

Lead_Manager Table:

Senior_Manager Table:

Manager Table:

Employee Table:

Sample Output

C1 Monika 1 2 1 2
C2 Samantha 1 1 2 2

Explanation
In company C1, the only lead manager is LM1. There are two senior managers, SM1 and SM2, under LM1. There is one manager, M1, under senior manager SM1. There are two employees, E1 and E2, under manager M1.

In company C2, the only lead manager is LM2. There is one senior manager, SM3, under LM2. There are two managers, M2 and M3, under senior manager SM3. There is one employee, E3, under manager M2, and another employee, E4, under manager, M3.

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💻 풀이

GROUP BY

SELECT
    C.company_code,
    C.founder,
    COUNT(DISTINCT(LM.lead_manager_code)),
    COUNT(DISTINCT(SM.senior_manager_code)),
    COUNT(DISTINCT(M.manager_code)),
    COUNT(DISTINCT(E.employee_code))
FROM Company AS C INNER JOIN Lead_Manager AS LM ON C.company_code = LM.company_code
    INNER JOIN Senior_Manager AS SM ON LM.lead_manager_code = SM.lead_manager_code
    INNER JOIN Manager AS M ON SM.senior_manager_code = M.senior_manager_code
    INNER JOIN Employee AS E ON M.manager_code = E.manager_code
GROUP BY C.company_code, C.founder
ORDER BY C.company_code ASC;

서브쿼리

SELECT
    C.company_code,
    C.founder,
    (SELECT COUNT(DISTINCT(LM.lead_manager_code)) FROM Lead_Manager AS LM
     WHERE C.company_code = LM.company_code),
    (SELECT COUNT(DISTINCT(SM.senior_manager_code)) FROM Senior_Manager AS SM
     WHERE C.company_code = SM.company_code),
    (SELECT COUNT(DISTINCT(M.manager_code)) FROM Manager AS M
     WHERE C.company_code = M.company_code),
    (SELECT COUNT(DISTINCT(E.employee_code)) FROM Employee AS E
     WHERE C.company_code = E.company_code)
FROM Company AS C
ORDER BY C.company_code ASC;

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💡 Idea

5개의 테이블을 연속적으로 JOIN한다.
GROUP BY 또는 서브쿼리를 이용하여 문제를 해결할 수 있다.
중복값을 제거한 고유값의 개수를 통해 결과 값을 도출해낼 수 있다.