Finding number of different workers in a month from

Question

Given the next table:

MonthYear          Name        Mission
-------------------------------------------
August 2016        Joe        Clean Table
August 2016        Joe        Clean Door
August 2016        Charles    Clean Table
September 2016     Joe        Clean Dorm
September 2016     Charles    Clean Kitchen
September 2016     Charles    Clean Roof
October 2016       Dominique  Clean Kitchen
October 2016       Dominique  Clean table

I need to know the number of people working per month. So, I need to generate the next table:

MonthYear                Number of Workers
-----------------------------------
August 2016               2
September 2016            2
October 2016              1

Answer 1

Basically group by MonthYear and count distinct workers.

select   MonthYear, count(distinct Name) as NumberOfWorkers
from     your_table
group by MontYear;