sql server 递归查询

摘要: sql server数据库通过CTE 提供递归查询， 关键字WITH

#1 创建测试表 tree：

create table tree (
id varchar(10),
parentId varchar(10),
node varchar(10)
)

#2 创建测试数据：

insert into tree values ('1', NULL, 'top')
insert into tree values ('21', '1', '2-1')
insert into tree values ('22', '1', '2-2')
insert into tree values ('3211', '21', '3-21-1')
insert into tree values ('3212', '21', '3-21-2')
insert into tree values ('3221', '22', '3-22-1')
insert into tree values ('3222', '22', '3-22-2')
insert into tree values ('43211', '3211', '4-3211-1')
insert into tree values ('43221', '3222', '4-3222-1')

说明：数据类似m叉树(m=2)的形式，不断扩展

#3 递归查询生成树的层级结构：

with cte(id, parentId, node, level)
as (
select id, parentId, node, 1 level from tree where parentId is null
union all
select b.id, b.parentId, b.node, level+1 from tree b inner join cte c on b.parentId = c.id
)
select id, parentId, node, level from cte order by level

结果如下：