数据库的递归查询
本文总结了postgres、mysql、oracle3种数据库的递归查询样例，包含向上递归和向下递归。
正文开始：
postgresql:
-
-- 向下递归
WITH RECURSIVE r AS (
SELECT * FROM digui_test WHERE id = 3
union ALL
SELECT digui_test.* FROM digui_test, r WHERE digui_test.pid = r.id
)
SELECT * FROM r ORDER BY id;-
-- 向下递归
WITH RECURSIVE r AS (
SELECT * FROM digui_test WHERE id = 3
union ALL
SELECT digui_test.* FROM digui_test, r WHERE digui_test.id = r.pid
)
SELECT * FROM r ORDER BY id;mysql:
5.7版本之前：
-
向上递归：
SELECT T2.id, T2.name ,T2.parent_id
FROM (
SELECT
@r AS _id,
(SELECT @r := parent_id FROM demo WHERE id = _id) AS parent_id,
@l := @l + 1 AS lvl
FROM
(SELECT @r := 2, @l := 0) vars,
demo h
WHERE @r > 0) T1
JOIN demo T2
ON T1._id = T2.id
ORDER BY T1.lvl DESC;-
向下递归：
SELECT
t3.id,t3.parent_id
FROM
(
SELECT
t1.id,
t1.parent_id,
IF
(
find_in_set( CONVERT ( parent_id USING utf8 ), @pids ) > 0,
@pids := concat( @pids, ',', id ),
0
) AS ischild
FROM
( SELECT id, parent_id FROM demo t ORDER BY parent_id, id ) t1,
( SELECT @pids := '1' ) t2
) t3
WHERE
ischild != 0
ORDER BY
t3.id;5.8版本之后：
-
向上递归：
WITH RECURSIVE r_t AS (
SELECT
s1.id,
s1.parent_id,
s1.name
FROM
demo s1
WHERE
s1.id = '1500098801490440193' UNION ALL
SELECT
s2.id,
s2.parent_id,
s2.name
FROM
demo s2
INNER JOIN r_t ON r_t.parent_id = s2.id
) SELECT
id,parent_id,name
FROM
r_t-
向下递归：
WITH RECURSIVE r_t AS (
SELECT `id`, `parent_id`, `name`
FROM `demo`
WHERE `id` = 1 -- where 1 is the parent_id
UNION ALL
SELECT `child`.`id`, `child`.`parent_id`, `child`.`name`
FROM `demo` `child`
JOIN `r_t` `parent` ON `child`.`parent_id` = `parent`.`id`
)
SELECT * FROM r_t;oracle:
select * from 表 start with 条件入口 connect by prior id = parent_id（向下）
select * from 表 start with 条件入口 connect by prior parent_id = id（向上）如果不写prior，表明前序遍历 未指明遍历方向，所以不进行递归，习惯上会在语句后面加上order by排序和group by分组
connect_by_root(列名) 查询根节点
connect_by_isleaf 查询是否叶子节点，0是，1不是
sys_connect_by_path 查询递归路径。
本文完...