tab1
name , count
A,1
B,1tab2
name,count
A,NULL
B,NULL
C,NULL
D,NULL在不改变tab2内容的情况下得到(将tab1中name和tab2匹配的值给tab2,不匹配赋值0)
A,1
B,1
C,0
D,0
name , count
A,1
B,1tab2
name,count
A,NULL
B,NULL
C,NULL
D,NULL在不改变tab2内容的情况下得到(将tab1中name和tab2匹配的值给tab2,不匹配赋值0)
A,1
B,1
C,0
D,0
from tab2
left join tab1 on tab2.name=tab1.name
tab2.name,isnull(tab1.[count],0) as [count]
from
tab2
left join tab1 on
tab2.name=tab1.name
from tab2
left join tab1 on tab2.name=tab1.name
if OBJECT_ID('tab1') is not null drop table tab1
create table tab1
(name varchar(10), [count] int)
if OBJECT_ID('tab2') is not null drop table tab2
create table tab2
(name varchar(10), [count] int)insert tab1 select 'A',1
insert tab1 select 'B',1
insert tab2 select 'A',NULL
insert tab2 select 'B',NULL
insert tab2 select 'C',NULL
insert tab2 select 'D',NULL
select tab2.name,isnull(tab1.[count],0) as [count]
from tab2
left join tab1 on tab2.name=tab1.name
name count
---------- -----------
A 1
B 1
C 0
D 0(4 行受影响)