sql关联查询问题

[strife013]

关联表a，b

a 有字段code
b 关联字段code

有个需求返回a表所有数据，
并且检查对应b中的code是否有对应值，如果有则加一列selected为true，否则自定义字段selected为

[wnf2009]

用left join

[zebraol]

select a.*, case when b.code is null then 'true' else 'false' end as selected
from a left join b
on a.code=b.code;

[strife013]

left join搞不定，要求是显示a表全部数据但是不能重复显示，就是说有3条数据就显示3条数据

[开着拖拉机泡妞]

[Quote=引用 2 楼 zebraol 的回复:]

select a.*, case when b.code is null then 'true' else 'false' end as selected
from a left join b
on a.code=b.code;
[/Quote]

貌似这个可以，试试，出问题再提出来

[tadoll]

select a.*, case when b.code is null then 'true' else 'false' end as selected
from a left join b
on a.code=b.code;

[tadoll]

select (' and '+case when 1=1 then 'c1 is null' else 'c1 is not null 'end) aa

[tadoll]

学习发帖，不会出那个sql框啊

[小和桑]

这个不是没有错误么？
[Quote=引用 2 楼 zebraol 的回复:]

select a.*, case when b.code is null then 'true' else 'false' end as selected
from a left join b
on a.code=b.code;
[/Quote]

[Page]

left join/right join/full join/inner join 都试试

[pengpeng409]

if object_id('[ta]')is not null
drop table ta
create table ta
(
acode varchar(20),
selected varchar(20)
)
insert into ta(acode,selected)
select '111',''
union all
select '222',''
union all
select '333',''

if object_id('[tb]')is not null
drop table tb
create table tb
(
bcode varchar(20)
)
insert into tb(bcode)
select '111'
union all
select '222'


select acode,case when acode=bcode then 'true'
else 'false' end as flag
from ta left join tb
on ta.acode=tb.bcode

[pengpeng409]

if object_id('[ta]')is not null
drop table ta
create table ta
(
acode varchar(20),
selected varchar(20)
)
insert into ta(acode,selected)
select '111',''
union all
select '222',''
union all
select '333',''

if object_id('[tb]')is not null
drop table tb
create table tb
(
bcode varchar(20)
)
insert into tb(bcode)
select '111'
union all
select '222'


select acode,case when acode=bcode then 'true'
else 'false' end as flag
from ta left join tb
on ta.acode=tb.bcode