how to update datetime column in sas

[MILKYLOVE]

I have a table in sas with a date column named DATE_MOD of format DATETIME23. 

The dates are as such:

28JAN2019:14:32:42

03JUN2021:14:22:13 

04JUN2021:16:02:23

Now I want to change the times in red and make them 23:59:59 for all the rows in this column like so:

28JAN2019:23:59:59

03JUN2021:23:59:59

04JUN2021:23:59:59

I use a proc sql update statement but it does not work. 

proc sql;
update operation 
set date_mod = dhms(date_mod,23,59,59);
quit;

Any help please?

[andreas_lds · Accepted solution]

One obvious issue: you have a datetime variable, but the function dhms expects a date as first argument.

Using a data step:

data want;
  set have;
  date_mod = dhms(datepart(date_mod), 23, 59, 59);
run;