How I can make left join work only when the number of records in the first table more or equal the number of records in the second table?

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SQL

I have tow table and I want do left join between them , But I want to left join happen only if the count of records that contain the same value of join column in the first table is more or equal the count of records that contain the same value of join column in the second table

what i try :

first i do the count of records per the each group

and then i put condition to filter (a.cnt>=b.cnt)

this is the code :

insert into work.discount_tmp 
select 
	SubsID , MSISDN , EppAcc, User_Name , Bill_Cycle, Tariff , Pack ,Discount_Qual_ID ,Discount_ID , Qualification_Type,Discount_Desc,Sequence,a.GroupID,RuleID,dib_band_id,dib_band_end,dib_charge_ref,DIB_DIS0,dib_disc_type,dib_limit_disc,DIB_MAX_,cd_class_type,ClassID,Class,dgh_group_id ,dgh_inclusion_from,dgh_inclusion_to,20191003 
from
(
	(
		select *, row_number() over (partition by GroupID order by Discount_ID ) as seqnum,
			COUNT(*) over (partition by GroupID order by GroupID ) as cnt 
		from 
			work.disc_band 
		where tbl_dt=20191003 
		order by Discount_ID
	) a
	left join
	(
		select *, row_number() over (partition by GroupID order by cd_class_type,try(cast(coalesce(classid,'0') as bigint)) ) as seqnum,
			count(*) over (partition by GroupID order by GroupID  ) as cnt 
		from 
			work.alltable1 
		where tbl_dt=20191003 
	) b 
	on 
	a.GroupID=b.GroupID  and a.cnt>=b.cnt and a.seqnum=b.seqnum   
 )

But my try not work because the join done first and then the condtion (so the value of cnt in the second table will not stay the same after join done )

any idea how to make that work ?

What I have tried:

insert into work.discount_tmp select SubsID , MSISDN , EppAcc, User_Name , Bill_Cycle, Tariff , Pack ,Discount_Qual_ID ,Discount_ID , Qualification_Type,Discount_Desc,Sequence,a.GroupID,RuleID,dib_band_id,dib_band_end,dib_charge_ref,DIB_DIS0,dib_disc_type,dib_limit_disc,DIB_MAX_,cd_class_type,ClassID,Class,dgh_group_id ,dgh_inclusion_from,dgh_inclusion_to,20191003 from
 ((select *, row_number() over (partition by GroupID order by Discount_ID ) as seqnum,
 COUNT(*) over (partition by GroupID order by GroupID ) as cnt from work.disc_band where tbl_dt=20191003 order by Discount_ID) a
 left join
 (select *, row_number() over (partition by GroupID order by cd_class_type,try(cast(coalesce(classid,'0') as bigint)) ) as seqnum,
 count(*) over (partition by GroupID order by GroupID  ) as cnt 
 from work.alltable1 where tbl_dt=20191003 ) b 
 on a.GroupID=b.GroupID  and a.cnt>=b.cnt and a.seqnum=b.seqnum   )