--alter proc question as 

declare @t table (scanCode varchar(6), dates datetime, flag varchar(1))

insert @t ( scanCode, dates, flag)
select '182086','01 Jul 2020','P' union all
select'182086','02 Jul 2020','P' union all
select'182086','03 Jul 2020','A' union all
select'182086','04 Jul 2020','A' union all
select'182086','06 Jul 2020','P' union all
select'182086','07 Jul 2020','P' union all
select'182086','08 Jul 2020','P' union all
select'182086','09 Jul 2020','P' union all
select'182086','10 Jul 2020','A' union all
select'182086','11 Jul 2020','A' union all
select'182086','13 Jul 2020','A' union all
select'182086','14 Jul 2020','A'


select scanCode
	, dates
	, flag
	, prn = row_number() over (partition by scanCode,flag order by scanCode, dates) 
from @t t
order by t.dates


--currently the result is

/*
scanCode	dates	flag	prn
182086		2020/07/01	P	1
182086		2020/07/02	P	2
182086		2020/07/03	A	1
182086		2020/07/04	A	2
182086		2020/07/06	P	3
182086		2020/07/07	P	4
182086		2020/07/08	P	5
182086		2020/07/09	P	6
182086		2020/07/10	A	3
182086		2020/07/11	A	4
182086		2020/07/13	A	5
182086		2020/07/14	A	6
*/

-- I want the result to be

/*
scanCode	dates	flag	prn
182086		2020/07/01	P	1
182086		2020/07/02	P	2
182086		2020/07/03	A	1
182086		2020/07/04	A	2
182086		2020/07/06	P	1
182086		2020/07/07	P	2
182086		2020/07/08	P	3
182086		2020/07/09	P	4
182086		2020/07/10	A	1
182086		2020/07/11	A	2
182086		2020/07/13	A	3
182086		2020/07/14	A	4
*/