MySQL 8.0

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create table a(puid int, pid int,systemcode char(10));
insert into a values(100,1003,'RG'),(200,1006,'CA'),(200,1007,'CA'),(300,1008,'RG');

create table b (euid int, lid int,systemcode char(10));
insert into b values(100,1003,'RG'),(100,1004,'RG'),(100,1005,'RG'),(200,1006,'CA'),
(300,1009,'RG')
select * from b


euid
lid
systemcode


100
1003
RG

100
1004
RG

100
1005
RG

200
1006
CA

300
1009
RG


select a.*
from (select a.*,
             count(b.euid) over (partition by a.puid) as num_matches
      from a left join
           b
           on a.puid = b.euid and a.pid = b.lid
     ) a
where num_matches = 0;


puid
pid
systemcode
num_matches


300
1008
RG
0