tab1 表结构：
create tab1 (
id int primary key identity(1,1),
parentid int not null,
name varchar(25)
)
递归语法（利用CTE表达式）：
1.根据父id递归查询子id
with tem1(id,parentid,name) as(
select id,parentid,name from tab1 where id = 1
union all
select tab1.id,tab1.parentid,tab1.name from tab1,tem1
where tab1.parentid = tem1.id
)
select * from tem1
2.根据子id递归查询父id
with tem1(id,parentid,name) as(
select id,parentid,name from tab1 where id = 1
union all
select tab1.id,tab1.parentid,tab1.name from tab1,tem1
where tab1.id= tem1.parentid
)
select * from tem1