declare @表1 table (c1 varchar(8),c2 varchar(10),c3 varchar(3),c4 varchar(3),c5 numeric(4,3))
insert into @表1
select 'P241799','GWP0800770','pc.','RMB',0.008 union all
select '201806','GWP0700225','pc.','HKD',0.06 union all
select 'PU300412',null,null,null,null

declare @表2 table (c1 varchar(8),c2 varchar(10),c3 varchar(3),c4 varchar(3),c5 numeric(4,3))
insert into @表2
select 'P241799',null,null,null,null union all
select '201806',null,null,null,null union all
select 'PU300412','ITP1000141','pc.','HKD',0.135

select 
ISNULL(a.c1,b.c1) AS c1,
ISNULL(a.c2,b.c2) AS c2,
ISNULL(a.c3,b.c3) AS c3,
ISNULL(a.c4,b.c4) AS c4,
ISNULL(a.c5,b.c5) AS c5
from @表1 a
LEFT JOIN @表2 b ON a.c1=b.c1

/*
c1       c2         c3   c4   c5
-------- ---------- ---- ---- ---------------------------------------
P241799  GWP0800770 pc.  RMB  0.008
201806   GWP0700225 pc.  HKD  0.060
PU300412 ITP1000141 pc.  HKD  0.135
*/