elect a.*, b.mail_pcs, b.mail_wgt from b left join a on a.flt=b.flt

------解决方案--------------------
SQL code
select a.*, b.mail_pcs, b.mail_wgt from b left join a on a.flt=b.flt

------解决方案--------------------
SQL code
select a.*, isnull(b.mail_pcs,0), insull(b.mail_wgt,0) from b left join a on a.flt=b.flt

------解决方案--------------------
SQL code

if object_id('a') is not null
   drop table a
go
create table a
(
 flt varchar(10),
 ori varchar(10),
 des varchar(10),
 pcs int,
 wgt int
)
go
insert into a
select 'cz0331','pek','los',10,100 union all
select 'cz0331','pek','dxb',20,200
go
if object_id('b') is not null
   drop table b
go
create table b
(
 flt varchar(10),
 mail_pcs int,
 mail_wgt int
)
go
insert into b
select 'cz0331',30,300
go
select t1.flt,ori,des,pcs,wgt,mail_pcs=isnull(mail_pcs,0),mail_wgt=isnull(mail_wgt,0) from (select * ,row=row_number() over(partition by flt order by getdate()) from a)t1 left join (select *,row=row_number() over(partition by flt order by getdate()) from b) t2
on t1.flt=t2.flt and t1.row=t2.row
go
/*
flt        ori        des        pcs         wgt         mail_pcs    mail_wgt
---------- ---------- ---------- ----------- ----------- ----------- -----------
cz0331     pek        los        10          100         30          300
cz0331     pek        dxb        20          200         0           0

(2 行受影响)
*/

------解决方案--------------------
探讨

SQL code

select a.*, isnull(b.mail_pcs,0), insull(b.mail_wgt,0) from b left join a on a.flt=b.flt