Php mysql查询以缩进子项并将所有子项分组

我有一个像这样的mysql表

id  Category         parent
2   Garments           12
3   Gents Garments          2
4   Sarees                  2
5   Bridal Sarees           4
6   IT                 12
7   IT Hardware         6
8   IT Software         6
9   Web Design          8
10  Web Based Solution  8
11  E-Commerce Solution 9
12  root                 NULL

使用mysql查询

SELECT t1.category AS lev1, t2.category as lev2, t3.category as lev3, 
t4.category as lev4
FROM categories AS t1
LEFT JOIN categories AS t2 ON t2.parent = t1.id
LEFT JOIN categories AS t3 ON t3.parent = t2.id
LEFT JOIN categories AS t4 ON t4.parent = t3.id
WHERE t1.category = 'root';

我能得到这个结果

lev1    lev2       lev3            lev4
root    Garments  Gents Garments   NULL
root    Garments  Sarees       Bridal Sarees
root    IT    IT Hardware      NULL
root    IT    IT Software      Web Design
root    IT    IT Software      Web Based Solution

现在我找不到一种方法来获取树状结构中单个列中的值。 范例

使用以下查询修改问题：

我已经部分实现了上述结果，但钢需要使用适当的分组 以下查询

SELECT distinct t1.category AS category
FROM categories AS t1
LEFT JOIN categories AS t2 ON t2.parent = t1.id
LEFT JOIN categories AS t3 ON t3.parent = t2.id
LEFT JOIN categories AS t4 ON t4.parent = t3.id
WHERE t1.category = 'root' 
union
SELECT distinct concat('--', t2.category) as category
FROM categories AS t1
LEFT JOIN categories AS t2 ON t2.parent = t1.id
LEFT JOIN categories AS t3 ON t3.parent = t2.id
LEFT JOIN categories AS t4 ON t4.parent = t3.id
WHERE t1.category = 'root'  
union

SELECT distinct  concat('----', t3.category) as category
FROM categories AS t1
LEFT JOIN categories AS t2 ON t2.parent = t1.id
LEFT JOIN categories AS t3 ON t3.parent = t2.id
LEFT JOIN categories AS t4 ON t4.parent = t3.id
WHERE t1.category = 'root' 
union
SELECT distinct concat('------', t4.category) as category
FROM categories AS t1
LEFT JOIN categories AS t2 ON t2.parent = t1.id
LEFT JOIN categories AS t3 ON t3.parent = t2.id
LEFT JOIN categories AS t4 ON t4.parent = t3.id
WHERE t1.category = 'root' 

我得到的结果是
根
--服装
--它
----男士服装
----纱丽
----IT硬件
----IT软件
------新娘礼服
------网页设计
------基于Web的解决方案
但是我想要的结果是
根
--服装
----男士服装
----纱丽
------新娘礼服
--它
----IT硬件
----IT软件
------网页设计

---

------基于Web的解决方案

如果您可以将表示层次结构的方式更改为可传递闭包表，那么您可以利用我过去给出的几个答案。主题是如何控制查询输出的排序，与上面描述的方法相同

---

这是您应该在表示层中处理的事情。

SELECT distinct t1.category AS category
FROM categories AS t1
LEFT JOIN categories AS t2 ON t2.parent = t1.id
LEFT JOIN categories AS t3 ON t3.parent = t2.id
LEFT JOIN categories AS t4 ON t4.parent = t3.id
WHERE t1.category = 'root' 
union
SELECT distinct concat('--', t2.category) as category
FROM categories AS t1
LEFT JOIN categories AS t2 ON t2.parent = t1.id
LEFT JOIN categories AS t3 ON t3.parent = t2.id
LEFT JOIN categories AS t4 ON t4.parent = t3.id
WHERE t1.category = 'root'  
union

SELECT distinct  concat('----', t3.category) as category
FROM categories AS t1
LEFT JOIN categories AS t2 ON t2.parent = t1.id
LEFT JOIN categories AS t3 ON t3.parent = t2.id
LEFT JOIN categories AS t4 ON t4.parent = t3.id
WHERE t1.category = 'root' 
union
SELECT distinct concat('------', t4.category) as category
FROM categories AS t1
LEFT JOIN categories AS t2 ON t2.parent = t1.id
LEFT JOIN categories AS t3 ON t3.parent = t2.id
LEFT JOIN categories AS t4 ON t4.parent = t3.id
WHERE t1.category = 'root'