select department_name, employee_name 
from departments join employees
on departments.department_id = employees.department_id;

select employee_name, salary, grade
from employees join grade
on employees.salary between grade.low and grade.high;

select substr(`Oracle Web問題集`, -6, 3)
from dual;

-- 引数で指定された文字列のm文字目以降からn回目に出現した検索文字列の先頭の位置を返す。
INSTR(文字列, 検索文字列, m, n)

select to_date('2021-5-21', 'YYYY-MM-DD')
from dual;

TO_DATE(
--------
12-05-21

select to_date('2012年5月21日', 'YYYY"年"MM"月"DD"日"')
from dual;

---TO_DATE
----------
--12-05-21