Oracle 11g Release 2

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declare
  var_P_DATE date := sysdate;
  v_last_day date;
begin
  v_last_day := last_day(var_P_DATE);
  dbms_output.put_line(to_char(v_last_day, 'YYYY-MM-DD HH24:MI:SS'));
  v_last_day := last_day(trunc(var_P_DATE));
  dbms_output.put_line(to_char(v_last_day, 'YYYY-MM-DD HH24:MI:SS'));
end;
/
1 rows affected

dbms_output:
2022-04-30 23:38:53
2022-04-30 00:00:00

declare
  var_P_DATE date := systimestamp;
  v_last_day date;
begin
  v_last_day := last_day(var_P_DATE);
  dbms_output.put_line(to_char(v_last_day, 'YYYY-MM-DD HH24:MI:SS'));
  v_last_day := last_day(trunc(var_P_DATE));
  dbms_output.put_line(to_char(v_last_day, 'YYYY-MM-DD HH24:MI:SS'));
end;
/
1 rows affected

dbms_output:
2022-04-30 23:38:53
2022-04-30 00:00:00

declare
  var_P_DATE date := sysdate;
begin
  dbms_output.put_line(var_P_DATE);
  dbms_output.put_line(to_char(var_P_DATE, 'YYYY-MM-DD HH24:MI:SS'));
end;
/
1 rows affected

dbms_output:
29-APR-22
2022-04-29 23:38:53

alter session set nls_date_format = 'DD/MM/YYYY'
declare
  var_P_DATE date := sysdate;
begin
  dbms_output.put_line(var_P_DATE);
  dbms_output.put_line(to_char(var_P_DATE, 'YYYY-MM-DD HH24:MI:SS'));
end;
/
1 rows affected

dbms_output:
29/04/2022
2022-04-29 23:38:53

alter session set nls_date_format = 'DD/MM/YYYY HH24:MI:SS'
declare
  var_P_DATE date := sysdate;
begin
  dbms_output.put_line(var_P_DATE);
  dbms_output.put_line(to_char(var_P_DATE, 'YYYY-MM-DD HH24:MI:SS'));
end;
/
1 rows affected

dbms_output:
29/04/2022 23:38:53
2022-04-29 23:38:53

alter session set nls_date_format = 'Day Month ddth YYYY "at" HH PM'
declare
  var_P_DATE date := sysdate;
begin
  dbms_output.put_line(var_P_DATE);
  dbms_output.put_line(to_char(var_P_DATE, 'YYYY-MM-DD HH24:MI:SS'));
end;
/
1 rows affected

dbms_output:
Friday    April     29th 2022 at 11 PM
2022-04-29 23:38:53