目錄

• 概述
• 1、數據準備
• 2 start with connect by prior遞歸查詢
• 2.1 查詢所有子節點
• 2.2 查詢所有父節點
• 2.3 查詢指定節點的根節點
• 2.4 查詢下行政組織遞歸路徑
• 3 with遞歸查詢
• 3.1 with遞歸子類
• 3.2 遞歸父類
• 4 MySQL 遞歸查找樹形結構
• 總結

概述

實際生活有很多樹形結構的數據，比如公司分為多個部門，部門下分為多個組，組下分為多個員工；省市縣的歸屬；頁面菜單欄等等。

如果想查詢某個節點的父節點或者子節點，一般通過表自身連接完成，但如果該節點的子節點還有多層結構，就需要使用遞歸調用。但如果數據量特別大，遞歸的次數指數級上升，而且查詢數據庫的次數也指數級上升，導致程序和數據庫壓力劇增，查詢時間特別長。那數據庫有沒有遞歸查詢語句呢？答案是肯定的。

start with connect by prior 遞歸查詢

1、數據準備

create table area_test(  id number(10) not null,  parent_id  number(10),  name       varchar2(255) not null);alter table area_test add (constraint district_pk primary key (id));insert into area_test (ID, PARENT_ID, NAME) values (1, null, "中國");insert into area_test (ID, PARENT_ID, NAME) values (11, 1, "河南省"); insert into area_test (ID, PARENT_ID, NAME) values (12, 1, "北京市");insert into area_test (ID, PARENT_ID, NAME) values (111, 11, "鄭州市");insert into area_test (ID, PARENT_ID, NAME) values (112, 11, "平頂山市");insert into area_test (ID, PARENT_ID, NAME) values (113, 11, "洛陽市");insert into area_test (ID, PARENT_ID, NAME) values (114, 11, "新鄉市");insert into area_test (ID, PARENT_ID, NAME) values (115, 11, "南陽市");insert into area_test (ID, PARENT_ID, NAME) values (121, 12, "朝陽區");insert into area_test (ID, PARENT_ID, NAME) values (122, 12, "昌平區");insert into area_test (ID, PARENT_ID, NAME) values (1111, 111, "二七區");insert into area_test (ID, PARENT_ID, NAME) values (1112, 111, "中原區");insert into area_test (ID, PARENT_ID, NAME) values (1113, 111, "新鄭市");insert into area_test (ID, PARENT_ID, NAME) values (1114, 111, "經開區");insert into area_test (ID, PARENT_ID, NAME) values (1115, 111, "金水區");insert into area_test (ID, PARENT_ID, NAME) values (1121, 112, "湛河區");insert into area_test (ID, PARENT_ID, NAME) values (1122, 112, "舞鋼市");insert into area_test (ID, PARENT_ID, NAME) values (1123, 112, "寶豐市");insert into area_test (ID, PARENT_ID, NAME) values (11221, 1122, "尚店鎮");

2 start with connect by prior遞歸查詢

• start with 子句：遍歷起始條件。如果要查父結點，這里可以用子結點的列，反之亦然。
• connect by 子句：連接條件。prior 跟父節點列parentid放在一起，就是往父結點方向遍歷；prior 跟子結點列subid放在一起，則往葉子結點方向遍歷。parent_id、id兩列誰放在 “=” 前都無所謂，關鍵是prior跟誰在一起。
• order by 子句：排序。

常用的select項：

LEVEL：級別
connect_by_root：根節點
sys_connect_by_path：遞歸路徑

2.1 查詢所有子節點

select t.*,LEVELfrom area_test tstart with name ="鄭州市"connect by prior id=parent_id

其實，如果單層結構，使用表自身連接也可以實現：

select * from area_test t1,area_test t2 where t1.PARENT_ID = t2.ID and t2.name="鄭州市";

當查詢節點下有多層數據：

select t.*,LEVELfrom area_test tstart with name ="河南省"connect by prior id=parent_id

select * from area_test t1,area_test t2 where t1.PARENT_ID = t2.ID and t2.name="河南省";

如果使用自身連接，也只能查到子一級節點的數據，需要遍歷子一級節點，遞歸查詢每個子一級節點下的子節點。明顯麻煩很多！！！

2.2 查詢所有父節點

select t.*,levelfrom area_test tstart with name ="鄭州市"connect by prior t.parent_id=t.idorder by level asc;

2.3 查詢指定節點的根節點

select d.*,	   connect_by_root(d.id) rootid,	   connect_by_root(d.name) rootnamefrom area_test dwhere name="二七區"start with d.parent_id IS NULLconnect by prior d.id=d.parent_id

select d.*,	   connect_by_root(d.id) rootid,	   connect_by_root(d.name) rootnamefrom area_test dstart with d.parent_id IS NULLconnect by prior d.id=d.parent_id

2.4 查詢下行政組織遞歸路徑

select id, parent_id, name, sys_connect_by_path(name, "->") namepath, levelfrom area_teststart with name = "平頂山市"connect by prior id = parent_id

3 with遞歸查詢

3.1 with遞歸子類

with tmp(id, parent_id, name) as (	select id, parent_id, name    from area_test    where name = "平頂山市"    union all    select d.id, d.parent_id, d.name    from tmp, area_test d    where tmp.id = d.parent_id   )select * from tmp;

3.2 遞歸父類

with tmp(id, parent_id, name) as  (   select id, parent_id, name   from area_test   where name = "二七區"   union all   select d.id, d.parent_id, d.name   from tmp, area_test d   where tmp.parent_id = d.id   )select * from tmp;

4 MySQL 遞歸查找樹形結構

參考文章：MySQL 遞歸查找樹形結構，這個方法太實用了

參考文章：Oracle遞歸查詢

總結

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