MySQL - 将表结果转换为行[重复]答案

【问题标题】：MySQL - convert table result into rows [duplicate]MySQL - 将表结果转换为行[重复]
【发布时间】：2013-12-23 16:00:40
【问题描述】：

我有一张这种格式的表格

id1 | id2 | id3 | id4  | id5
a   | b   | c   | null | null
a   | b   | d   | null | null
a   | b   |null | null | null

我需要得到结果(a,b,c,d)

我是用php做的，但是代码太难了……

    <?php
    $sql="SELECT t1.id as id1, t2.id AS id2, t3.id AS id3, t4.id AS id4, t5.id AS id5
    FROM store_subcategory AS t1
    LEFT JOIN store_subcategory AS t2 ON t2.parent_id = t1.id
    LEFT JOIN store_subcategory AS t3 ON t3.parent_id = t2.id
    LEFT JOIN store_subcategory AS t4 ON t4.parent_id = t3.id
    LEFT JOIN store_subcategory AS t5 ON t5.parent_id = t4.id
    WHERE (t1.root_id=$cat or t1.id=$cat) and t1.store_id=$id";

    $result=$mysqli->query($sql);
    $subid=array();
    while($row=$result->fetch_assoc())
    {
        if($row["id1"]!=null) $subid[$row["id1"]]=1;
        if($row["id2"]!=null) $subid[$row["id2"]]=1;
        if($row["id3"]!=null) $subid[$row["id3"]]=1;
        if($row["id4"]!=null) $subid[$row["id4"]]=1;
        if($row["id5"]!=null) $subid[$row["id5"]]=1;
    }
    $subsarray=array();
    foreach($subid as $key => $value)
    {
        array_push($subsarray, $key);
    }
    $subid=implode(",", $subsarray);
    ?>

谢谢 PS：对不起我的英语不好

编辑：该表用于具有 5 个级别的分层树

`store_subcategory` (
  `id` int(11) NOT NULL AUTO_INCREMENT,
  `parent_id` int(11) DEFAULT NULL,
  `it` varchar(255) NOT NULL,
  PRIMARY KEY (`id`)

编辑2：解决方案可能是这样的

SELECT * FROM (
SELECT DISTINCT(t1.id)
    FROM store_subcategory AS t1
    WHERE (t1.root_id=$cat or t1.id=$cat) and t1.store_id=$id
UNION
SELECT DISTINCT(t2.id)
    FROM store_subcategory AS t1
    LEFT JOIN store_subcategory AS t2 ON t2.parent_id = t1.id
    WHERE (t1.root_id=$cat or t1.id=$cat) and t1.store_id=$id
UNION
SELECT DISTINCT(t3.id)
    FROM store_subcategory AS t1
    LEFT JOIN store_subcategory AS t2 ON t2.parent_id = t1.id
    LEFT JOIN store_subcategory AS t3 ON t3.parent_id = t2.id
    WHERE (t1.root_id=$cat or t1.id=$cat) and t1.store_id=$id
UNION
SELECT DISTINCT(t4.id)
    FROM store_subcategory AS t1
    LEFT JOIN store_subcategory AS t2 ON t2.parent_id = t1.id
    LEFT JOIN store_subcategory AS t3 ON t3.parent_id = t2.id
    LEFT JOIN store_subcategory AS t4 ON t4.parent_id = t3.id
    WHERE (t1.root_id=$cat or t1.id=$cat) and t1.store_id=$id
UNION
SELECT DISTINCT(t5.id)
    FROM store_subcategory AS t1
    LEFT JOIN store_subcategory AS t2 ON t2.parent_id = t1.id
    LEFT JOIN store_subcategory AS t3 ON t3.parent_id = t2.id
    LEFT JOIN store_subcategory AS t4 ON t4.parent_id = t3.id
    LEFT JOIN store_subcategory AS t5 ON t5.parent_id = t4.id
    WHERE (t1.root_id=$cat or t1.id=$cat) and t1.store_id=$id
) AS t_group WHERE id IS NOT NULL

【问题讨论】：

标签： php mysql sql

【解决方案1】：

我不知道这个数据结构有什么用，但听起来你想要这样的东西：

SELECT DISTINCT(ID) 
FROM 
    (select distinct(id1) AS ID
    from table
    UNION
    select distinct(id2) AS ID
    from table
    UNION
    select distinct(id3) AS ID
    from table)

【讨论】：