Next_day () function parsing in oracle

In oracle, The next_day () function parses the SQL code. The select next_day (sysdate, 1) from dual NEXT_DAY (date, char) date parameter for the next Monday of the current system time is of the date type, char: 1 ~ 7 or Monday/Mon ~ Sunday/www.2cto.com specifies the date of the next week (specified by char), char can also be 1 ~ Replace 7. 1 indicates Sunday, and 2 indicates Monday .... It can also be Monday or Tuesday... Sunday SQL code select next_day (sysdate, 'sunday') from dual; SQL code SQL> select NEXT_DAY (sysdate, 'monday') FROM DUAL; select NEXT_DAY (sysdate, 'monday ') from dual ORA-01846: week-day invalid SQL> alter session set NLS_DATE_LANGUAGE = American; Session altered www.2cto.com SQL> select NEXT_DAY (sysdate, 'monday') FROM DUAL; ② SQL> select NEXT_DAY (sysdate, 'mon') FROM DUAL; the date found at ① and ② is the same, and the date + current system time is different in minutes and seconds.