1.以左边为显示表，从其他表查询关联的数据（多表查询）
select a.*,b.name from da as a left join db as b on a.id = b.pid
left join dc as c on a.nameid = b.id
2.取一条数据
select * from da where rownum=1
1.以左边为显示表，从其他表查询关联的数据（多表查询）
select a.*,b.name from da as a left join db as b on a.id = b.pid
left join dc as c on a.nameid = b.id
2.取一条数据
select * from da where rownum=1