[TIP] SELECT 절 서브쿼리 사용시 주의점

이렇게 수행 시 에러 발생함.

select a.employee_id, a.first_name||' '||a.last_name names, (select b.department_name

from employees a, departments b

where a.department_id = b.department_id) dep_names

from employees a

where a.department_id = 100;

ORA-01427: single-row subquery returns more than one row

01427. 00000 -  "single-row subquery returns more than one row"

*Cause:    

*Action:

--> 요렇게 고쳐서 수행해야 함

select a.employee_id, a.first_name||' '||a.last_name names, (select b.department_name

from departments b

where a.department_id = b.department_id) dep_names

from employees a

where a.department_id = 100;