=COUNTIF(A1:A100,"March")

if the month and employees match 1:1 and the month is a name not a date.
Otherwise

=SUMPRODUCT(--(MONTH(A1:A100)=3),--(B1:B100<""))

--

HTH

RP
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"Expert N" <Expert wrote in message
...
How to count unique values of a column corresponding to a respective
repeated
values of a column. For example there are multiple month entries in a
column,
and for every month entry there are multiple employee names. How to count
the
number of employees in a month.