On the script or on the front-end, you can create derived fields (Year field and Month field) using your Date field.
if your Date field is on this format: DD/MM/YYYY
Date(FIELD,'YYYY') as YEAR
Date(FIELD,'MM') as MONTH
Date(Date#(FIELD,'DD/MM/YYYY'),'YYYY') as YEAR
Date(Date#(FIELD,'DD/MM/YYYY'),'MM') as MONTH
It appears to me that DATE_REVIEW_ASSIGNED is not a date, but a text.
If so, you coud try this in the script:
Date(Date#(DATE_REVIEW_ASSIGNED,'DD-MMM-YYYY hh.mm.ss')) as DATE_REVIEW_ASSIGNED
then you can apply month() and year() functions in the script (same LOAD istruction):
year(Date#(DATE_REVIEW_ASSIGNED,'DD-MMM-YYYY hh.mm.ss')) as vYEAR
month(Date#(DATE_REVIEW_ASSIGNED,'DD-MMM-YYYY hh.mm.ss')) as vMONTH
Else, after you have loaded in the script DATE_REVIEW_ASSIGNED as a date, you can operate in front end with year() and month() function:
The two new calculated fields need to be the part that they are supposed to be - namely that YEAR becomes a year and not a full date and MONTH becomes a month and not a full date:
Year( DATE_REVIEW_ASSIGNED ) AS YEAR_REVIEW_ASSIGNED,
Month( DATE_REVIEW_ASSIGNED ) AS MONTH_REVIEW_ASSIGNED,
Only in that way they can be used as grouping mechanisms to calculate something for the entire year or month or year by month and so forth.
So what you have in your script screenshot from lines 156 to 157 is correct. Mind you that the v prefix you put on the resulting field names is what you normally only would use with variables - as a coding standard. Don't confuse fields with variables as they are two entirely different things. What you are dealing with here is purely fields - not variables.