帮写一条两个表连接的语句
表usermessage(id,username,password,touxiang)和表table20(id,username,title,time,content)，
其中usermessage和table20中有一共同字段username，
现在我想得到这样的结果：显示 表A的username,touxiang，表B的title、time、content ，
where条件是根据table20的id来查询，传入的参数是string id4
大概代码如下：
string SqlStr4="select username,touxiang,title,time,content from usermessage and table20 where table20.id='"+id4+"'";
select a.username,a.touxiang,b.title,b.time,b.content from usermessage a
left join table20 b on a.username=b.username
where b.id=
select a.username,a.touxiang,b.title,b.time,b.content from usermessage a
left join table20 b on a.username=b.username
where b.id=
string SqlStr4="select a.username,a.touxiang,b.title,b.time,b.content from usermessage a,table20 b where a.username=b.username and b.id='"+id4+"'";
SELECT a.username ,
a.touxiang ,
b.title ,
b.time ,
b.content
FROM usermessage a
INNER JOIN table20 b ON A.username = b.username
WHERE b.id = @id
select username,touxiang,title,time,content
from usermessage a left join table20 b
on a.id=b.id and a.username=b.username
where b.id='"+id4+"'"
