SELECT DAY_DATE,to_char(DAY_DATE,'fmday') weekday
FROM(
SELECT TO_DATE('2021-01-01', 'yyyy-mm-dd') + ROWNUM - 1 DAY_DATE
FROM DUAL
CONNECT BY ROWNUM <= TO_DATE('2021-12-31', 'yyyy-mm-dd') - TO_DATE('2021-01-01', 'yyyy-mm-dd')+ 1)
WHERE to_char(DAY_DATE,'fmday') = 'monday'