can i can use two group by in sql query

Posted on by Wyatt Peters

I have these two tables:

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 these SQL statements, but I was unable to bring them together:

SELECT StaffId, COUNT(*) AS covidCount 
FROM Covids 
GROUP BY StaffId

SELECT WorkHours 
FROM WorkingHours 
GROUP BY WorkHours