Find duplicate values starting with some specific cahrecter

Quote:

i know how to find duplicate values using count() but my question is how can i find duplicate values starting with some letter like'A' or 'K'

i have a table tblmytable like this

id rollnumber city fess
1 A100156 Ajamer 450
2 P102555 Pune 450
3 A100156 Ajamer 450
4 P102555 Pune 450

select rollnumber,count(rollnumber) AS COUNTOF from tblmytable group by rollnumber having count(rollnumber)>1 order by rollnumber

gives me this result

rollnumber countof

A100156 2
P102555 2

i want to find duplicate roll numbers starting with 'A'

like this how can i modify the query

select rollnumber,count(rollnumber) AS COUNTOF from tblmytable group by rollnumber having count(rollnumber)>1 order by rollnumber