SQL Server 2005开始，我们可以直接通过CTE来支持递归查询,CTE即公用表表达式
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公用表表达式（CTE），是一个在查询中定义的临时命名结果集将在from子句中使用它。每个CTE仅被定义一次（但在其作用域内可以被引用任意次），并且在该查询生存期间将一直生存。可以使用CTE来执行递归操作。创建的语法是：
with <name of you cte>(<column names>)
as( <actual query> )
select * from <name of your cte>
1、生成数据
--菜单目录结构表
create table tb_menu(
id int not null, --主键id
title varchar(50), --标题
parent int --parent id
);
--父菜单
insert into tb_menu(id, title, parent) values(1, '父菜单1',null);
insert into tb_menu(id, title, parent) values(2, '父菜单2',null);
insert into tb_menu(id, title, parent) values(3, '父菜单3',null);
insert into tb_menu(id, title, parent) values(4, '父菜单4',null);
insert into tb_menu(id, title, parent) values(5, '父菜单5',null);
--一级菜单
insert into tb_menu(id, title, parent) values(6, '一级菜单6',1);
insert into tb_menu(id, title, parent) values(7, '一级菜单7',1);
insert into tb_menu(id, title, parent) values(8, '一级菜单8',1);
insert into tb_menu(id, title, parent) values(9, '一级菜单9',2);
insert into tb_menu(id, title, parent) values(10, '一级菜单10',2);
insert into tb_menu(id, title, parent) values(11, '一级菜单11',2);
insert into tb_menu(id, title, parent) values(12, '一级菜单12',3);
insert into tb_menu(id, title, parent) values(13, '一级菜单13',3);
insert into tb_menu(id, title, parent) values(14, '一级菜单14',3);
insert into tb_menu(id, title, parent) values(15, '一级菜单15',4);
insert into tb_menu(id, title, parent) values(16, '一级菜单16',4);
insert into tb_menu(id, title, parent) values(17, '一级菜单17',4);
insert into tb_menu(id, title, parent) values(18, '一级菜单18',5);
insert into tb_menu(id, title, parent) values(19, '一级菜单19',5);
insert into tb_menu(id, title, parent) values(20, '一级菜单20',5);
--二级菜单
insert into tb_menu(id, title, parent) values(21, '二级菜单21',6);
insert into tb_menu(id, title, parent) values(22, '二级菜单22',6);
insert into tb_menu(id, title, parent) values(23, '二级菜单23',7);
insert into tb_menu(id, title, parent) values(24, '二级菜单24',7);
insert into tb_menu(id, title, parent) values(25, '二级菜单25',8);
insert into tb_menu(id, title, parent) values(26, '二级菜单26',9);
insert into tb_menu(id, title, parent) values(27, '二级菜单27',10);
insert into tb_menu(id, title, parent) values(28, '二级菜单28',11);
insert into tb_menu(id, title, parent) values(29, '二级菜单29',12);
insert into tb_menu(id, title, parent) values(30, '二级菜单30',13);
insert into tb_menu(id, title, parent) values(31, '二级菜单31',14);
insert into tb_menu(id, title, parent) values(32, '二级菜单32',15);
insert into tb_menu(id, title, parent) values(33, '二级菜单33',16);
insert into tb_menu(id, title, parent) values(34, '二级菜单34',17);
insert into tb_menu(id, title, parent) values(35, '二级菜单35',18);
insert into tb_menu(id, title, parent) values(36, '二级菜单36',19);
insert into tb_menu(id, title, parent) values(37, '二级菜单37',20); --三级菜单
insert into tb_menu(id, title, parent) values(38, '三级菜单38',21);
insert into tb_menu(id, title, parent) values(39, '三级菜单39',22);
insert into tb_menu(id, title, parent) values(40, '三级菜单40',23);
insert into tb_menu(id, title, parent) values(41, '三级菜单41',24);
insert into tb_menu(id, title, parent) values(42, '三级菜单42',25);
insert into tb_menu(id, title, parent) values(43, '三级菜单43',26);
insert into tb_menu(id, title, parent) values(44, '三级菜单44',27);
insert into tb_menu(id, title, parent) values(45, '三级菜单45',28);
insert into tb_menu(id, title, parent) values(46, '三级菜单46',28);
insert into tb_menu(id, title, parent) values(47, '三级菜单47',29);
insert into tb_menu(id, title, parent) values(48, '三级菜单48',30);
insert into tb_menu(id, title, parent) values(49, '三级菜单49',31);
insert into tb_menu(id, title, parent) values(50, '三级菜单50',31);
commit;
2.查找所有上级节点
--查询树状结构某节点(44)的上级所有根节点
with cte_parent(id,title,parent)
as
(
--起始条件
select id,title,parent
from tb_menu
where id = 44 --列出子节点查询条件
union all
--递归条件
select a.id,a.title,a.parent
from tb_menu a
inner join
cte_parent b --执行递归，这里就要理解下了
on a.id=b.parent
)
select * from cte_parent;
3、查找下级节点带level
--查询树状结构某节点下的所有子节点(
with cte_child(id,title,parent,level)
as
(
--起始条件
select id,title,parent,0 as level
from tb_menu
where id = 6--列出父节点查询条件
union all
--递归条件
select a.id,a.title,a.parent,b.level+1
from tb_menu a
inner join
cte_child b
on ( a.parent=b.id)
)
select * from cte_child;