MySQL层次结构数据抽取

还有一件事需要考虑,关系数据库并不是存储分层数据的最理想、最自然的方式。像您这里这样的结构(本质上是一个二叉树)将更容易用XML blob表示,您可以将其持久化,或者作为对象存储在面向对象的数据库中。

对你来说最简单的方法就是在保持深度的地方添加一个列。 否则查询将非常低效-您将必须获得整个层次结构,并按左数排序(这将把第一个子节点放在第一位),将其连接到自身以确保对于每个下一个节点,左数等于上一个节点的右数+1

通常,嵌套间隔算法很好,但有一个严重的缺点-如果您向树中添加一些内容,则需要大量重新计算。 一个很好的替代方法是Tropashko嵌套区间算法和连续分数-只是谷歌为它。用这种算法得到低于父级的一个级别是很自然的。此外,给定一个子对象,可以计算其所有父对象的所有数字,而无需访问数据库。

我更喜欢邻接表的方式。下面的示例使用一个非递归存储过程返回一个树/子树,然后我将其转换为一个XML DOM,但是您可以对resultset执行任何您喜欢的操作。记住,这是从PHP到MySQL的一次调用,而且邻接列表更易于管理。

完整脚本如下: http://pastie.org/1294143

菲律宾比索

<?php

header("Content-type: text/xml");

$conn = new mysqli("localhost", "foo_dbo", "pass", "foo_db", 3306);

// one non-recursive db call to get the tree

$result = $conn->query(sprintf("call department_hier(%d,%d)", 2,1));

$xml = new DomDocument;
$xpath = new DOMXpath($xml);

$dept = $xml->createElement("department");
$xml->appendChild($dept);

// loop and build the DOM

while($row = $result->fetch_assoc()){

    $staff = $xml->createElement("staff");
    // foreach($row as $col => $val) $staff->setAttribute($col, $val); 

    $staff->setAttribute("staff_id", $row["staff_id"]); 
    $staff->setAttribute("name", $row["name"]); 
    $staff->setAttribute("parent_staff_id", $row["parent_staff_id"]); 

    if(is_null($row["parent_staff_id"])){
        $dept->setAttribute("dept_id", $row["dept_id"]); 
        $dept->setAttribute("department_name", $row["department_name"]); 
        $dept->appendChild($staff);
    }
    else{
        $qry = sprintf("//*[@staff_id = '%d']", $row["parent_staff_id"]);
        $parent = $xpath->query($qry)->item(0);
        if(!is_null($parent)) $parent->appendChild($staff);
    }
}
$result->close();
$conn->close();

echo $xml->saveXML();
?>

XML输出

<department dept_id="2" department_name="Mathematics">
    <staff staff_id="1" name="f00" parent_staff_id="">
        <staff staff_id="5" name="gamma" parent_staff_id="1"/>
        <staff staff_id="6" name="delta" parent_staff_id="1">
            <staff staff_id="7" name="zeta" parent_staff_id="6">
                <staff staff_id="2" name="bar" parent_staff_id="7"/>
                <staff staff_id="8" name="theta" parent_staff_id="7"/>
            </staff>
        </staff>
    </staff>
</department>

SQL资料

-- TABLES

drop table if exists staff;
create table staff
(
staff_id smallint unsigned not null auto_increment primary key,
name varchar(255) not null
)
engine = innodb;

drop table if exists departments;
create table departments
(
dept_id tinyint unsigned not null auto_increment primary key,
name varchar(255) unique not null
)
engine = innodb;

drop table if exists department_staff;
create table department_staff
(
dept_id tinyint unsigned not null,
staff_id smallint unsigned not null,
parent_staff_id smallint unsigned null,
primary key (dept_id, staff_id),
key (staff_id),
key (parent_staff_id)
)
engine = innodb;

-- STORED PROCEDURES

drop procedure if exists department_hier;

delimiter #

create procedure department_hier
(
in p_dept_id tinyint unsigned,
in p_staff_id smallint unsigned
)
begin

declare v_done tinyint unsigned default 0;
declare v_dpth smallint unsigned default 0;

create temporary table hier(
 dept_id tinyint unsigned,
 parent_staff_id smallint unsigned, 
 staff_id smallint unsigned, 
 depth smallint unsigned
)engine = memory;

insert into hier select dept_id, parent_staff_id, staff_id, v_dpth from department_staff 
    where dept_id = p_dept_id and staff_id = p_staff_id;

/* http://dev.mysql.com/doc/refman/5.0/en/temporary-table-problems.html */

create temporary table tmp engine=memory select * from hier;

while not v_done do

    if exists( select 1 from department_staff e 
            inner join hier on e.dept_id = hier.dept_id and e.parent_staff_id = hier.staff_id and hier.depth = v_dpth) then

        insert into hier select e.dept_id, e.parent_staff_id, e.staff_id, v_dpth + 1 from department_staff e 
            inner join tmp on e.dept_id = tmp.dept_id and e.parent_staff_id = tmp.staff_id and tmp.depth = v_dpth;

        set v_dpth = v_dpth + 1;            

        truncate table tmp;
        insert into tmp select * from hier where depth = v_dpth;

    else
        set v_done = 1;
    end if;

end while;

select 
 hier.dept_id,
 d.name as department_name,
 s.staff_id,
 s.name,
 p.staff_id as parent_staff_id,
 p.name as parent_name,
 hier.depth
from 
 hier
inner join departments d on hier.dept_id = d.dept_id
inner join staff s on hier.staff_id = s.staff_id
left outer join staff p on hier.parent_staff_id = p.staff_id;

drop temporary table if exists hier;
drop temporary table if exists tmp;

end #

delimiter ;

-- TEST DATA

insert into staff (name) values 
    ('f00'),('bar'),('alpha'),('beta'),('gamma'),('delta'),('zeta'),('theta');

insert into departments (name) values
 ('Computing'),('Mathematics'),('English'),('Engineering'),('Law'),('Music');

insert into department_staff (dept_id, staff_id, parent_staff_id) values
(1,1,null), 
    (1,2,1), 
    (1,3,1), 
        (1,4,3),
            (1,7,4),
(2,1,null), 
    (2,5,1), 
    (2,6,1), 
        (2,7,6),
            (2,8,7),
            (2,2,7);

-- TESTING (call this sproc from your php)

call department_hier(1,1);

call department_hier(2,1);