데이터 분석 기술 블로그

SolutionSELECT e.employee_idFROM Employees eLEFT JOIN Employees mON e.manager_id = m.employee_idWHERE (e.salary

SolutionSELECT ROUND(AVG(POPULATION))FROM CITY;

SolutionSELECT *, (CASE WHEN x + y   * 삼각형의 조건 : 제일 긴 변이 나머지 두 변의 합보다 작아야 한다.

SolutionSELECT AVG(POPULATION)FROM CITYWHERE DISTRICT = 'California';

SolutionSELECT employee_id, department_idFROM EmployeeWHERE primary_flag = 'Y' OR employee_id IN (SELECT employee_id FROM Employee GROUP BY employee_id HAVING COUNT(department_id) = 1); 1차 시도처음에는 예시만 보고 'primary_flag'가 'Y'이거나 employee_id = department_id인 데이터를 추출하려고 했으나 오답이었고 후자가 항상 맞지는 않다는 것을 알았다. 2차 시도SELECT employee_id, department_idFROM EmployeeWHERE primary_flag = 'Y'..

SolutionSELECT SUM(POPULATION)FROM CITYWHERE DISTRICT = 'California';

SolutionSELECT e.employee_id, e.name, COUNT(r.employee_id) AS reports_count, ROUND(AVG(r.age), 0) AS average_ageFROM Employees eJOIN Employees rON e.employee_id = r.reports_toGROUP BY e.employee_id, e.nameORDER BY e.employee_id; 처음에는 다 구할 수 있었지만 reports_to에 대응하는 name을 찾을 수 없어서 검색해야만 했다. 확인해 보니 간단하게 JOIN으로 해결할 수 있었다...

SolutionSELECT COUNT(ID)FROM CITYWHERE POPULATION > 100000;