本文给大家介绍有关数据库SQL递归查询在不同数据库中的实现方法，具体内容请看下文。
比如表结构数据如下：
Table:Tree
ID Name ParentId
1一级 0
2 二级1
3 三级2
4四级3
SQL SERVER 查询方法:
//上查
with tmpTree
as
(
select * from Tree where Id=2
union all
select p.* from tmpTree inner join Tree p on p.Id=tmpTree.ParentId
)
select * from tmpTree
//下查
with tmpTree
as
(
select * from Tree where Id=2
union all
select s.* from tmpTree inner join Tree s on s.ParentId=tmpTree.Id
)
select * from tmpTree
SQL SERVER 及以后版本，还可用如下方法：
增加一列TID,类型设为：hierarchyid(这个是CLR类型，表示层级)，且取消ParentId字段，变成如下：(表名为：Tree2)
TIdIdName
0x 1 一级
0x58 2二级
0x5B403三级
0x5B5E4四级
查询方法：
SELECT *,TId.GetLevel() as [level] FROM Tree2 --获取所有层级
DECLARE @ParentTree hierarchyid
SELECT @ParentTree=TId FROM Tree2 WHERE Id=2
SELECT *,TId.GetLevel()AS [level] FROM Tree2 WHERE TId.IsDescendantOf(@ParentTree)=1 --获取指定的节点所有下级
DECLARE @ChildTree hierarchyid
SELECT @ChildTree=TId FROM Tree2 WHERE Id=3
SELECT *,TId.GetLevel()AS [level] FROM Tree2 WHERE @ChildTree.IsDescendantOf(TId)=1 --获取指定的节点所有上级
ORACLE中的查询方法：
SELECT *
FROM Tree
START WITH Id=2
CONNECT BY PRIOR ID=ParentId --下查
SELECT *
FROM Tree
START WITH Id=2
CONNECT BY ID= PRIOR ParentId --上查
MYSQL 中的查询方法：
//定义一个依据ID查询所有父ID为这个指定的ID的字符串列表，以逗号分隔
CREATE DEFINER=`root`@`localhost` FUNCTION `getChildLst`(rootId int,direction int) RETURNS varchar(1000) CHARSET utf8
BEGIN
DECLARE sTemp VARCHAR(5000);
DECLARE sTempChd VARCHAR(1000);
SET sTemp = '$';
IF direction=1 THEN
SET sTempChd =cast(rootId as CHAR);
ELSEIF direction=2 THEN
SELECT cast(ParentId as CHAR) into sTempChd FROM Tree WHERE Id=rootId;
END IF;
WHILE sTempChd is not null DO
SET sTemp = concat(sTemp,',',sTempChd);
SELECT group_concat(id) INTO sTempChd FROM Tree where (direction=1 and FIND_IN_SET(ParentId,sTempChd)>0)
or (direction=2 and FIND_IN_SET(Id,sTempChd)>0);
END WHILE;
RETURN sTemp;
END
//查询方法：
select * from tree where find_in_set(id,getChildLst(1,1));--下查
select * from tree where find_in_set(id,getChildLst(1,2));--上查
补充说明：上面这个方法在下查是没有问题，但在上查时会出现问题，原因在于我的逻辑写错了，存在死循环，现已修正，新的方法如下：
CREATE DEFINER=`root`@`localhost` FUNCTION `getChildLst`(rootId int,direction int) RETURNS varchar(1000) CHARSET utf8
BEGIN
DECLARE sTemp VARCHAR(5000);
DECLARE sTempChd VARCHAR(1000);
SET sTemp = '$';
SET sTempChd =cast(rootId as CHAR);
IF direction=1 THEN
WHILE sTempChd is not null DO
SET sTemp = concat(sTemp,',',sTempChd);
SELECT group_concat(id) INTO sTempChd FROM Tree where FIND_IN_SET(ParentId,sTempChd)>0;
END WHILE;
ELSEIF direction=2 THEN
WHILE sTempChd is not null DO
SET sTemp = concat(sTemp,',',sTempChd);
SELECT group_concat(ParentId) INTO sTempChd FROM Tree where FIND_IN_SET(Id,sTempChd)>0;
END WHILE;
END IF;
RETURN sTemp;
END
这样递归查询就很方便了。
