can i can use two group by in sql query

Hi i have two table

  Covids
    | CovidId | StaffId | CovidStartDate | CovidFinishDate | 
      -------   -------   --------------   ---------------
        1           1       21.01.2021         15.01.2021
        2           1       26.04.2021         16.04.2021
        3           2       21.02.2021         14.01.2021
        4           3       22.03.2021         17.03.2021
        5           3       15.04.2021         30.04.2021
  
   WorkingHours
    | WorkId | StaffId | WorkHours| 
     -------   -------   ---------
        1          1          8
        2          2          9
        3          3          8

I want to show how many times they had covid by working hour
expected result

    | WorkHour | CovidCount| 
     -------      -------   
        8           4          
        9           1          
             

i wrote this but i didn’t unite

Select StaffId,Count(*) as covidCount From Covids group by StaffId
Select WorkHours From WorkingHours group by WorkHours

>Solution :

Of course two separate queries won’t "unite". You need to join the tables and then do the aggregation.

SELECT w.workhours AS workhour,
       count(*) AS covidcount
       FROM workinghours AS w
            LEFT JOIN covids AS c
                      ON c.staffid = w.staffid
       GROUP BY w.workhours;