SQL (JOIN)

문제내용

 

Animal_ins , Animal_outs 두개의 테이블에서 공통적인 컬럼을 찾아서 그 해당 컬럼에 내용을 조회하는 SQL

 

LEFT JOIN

 Table#1

 

EmployeeID	EmployeeName
1	Alice
2	Bob
3	charlis

Table#2 

 

DepartmentID	EmployeeID	DepartmentName
101	1	HR
102	2	Engineering

 

SELECT Employees.EmployeeID, Employees.EmployeeName, Departments.DepartmentName

FROM Employees

LEFT JOIN Departments

ON Employees.EmployeeID = Departments.EmployeeID;

 

 결과

 

EmployeeID	EmployeeName	DepartmentName
1	Alice	HR
2	Bob	Engineering
3	Charlie	NULL

 

 

문제 정답

SELECT ANIMAL_INS.NAME, ANIMAL_INS.DATETIME

FROM ANIMAL_INS

LEFT JOIN ANIMAL_OUTS

ON ANIMAL_INS.ANIMAL_ID = ANIMAL_OUTS.ANIMAL_ID WHERE ANIMAL_OUTS.ANIMAL_ID IS NULL

ORDER BY ANIMAL_INS.DATETIME ASC

LIMIT 3;