从数据透视 table（垂直 mysql table）查看数据

Question

我对枢轴table真的很困惑，请看看我有什么以及我需要实现什么：

这是我的mysqltable结构

id  meta_value            field_id   item_id

1   Ankur                 Fname      1
2   Gupta                 Lname      1
3   AAS Holdings          Company    1
4   Christie              Fname      2
5   Trojillo              Lname      2
6   AWS                   Company    2
7   Devadanam             Fname      3
8   Pulukuri              Lname      3
9   AAS Holdings          Company    3
10  Radha                 Fname      4
11  Neupane               Lname      4
......> There is no "Company" for that person
12  Marites               Fname      5
13  Torsar                Lname      5
14  AAS Holdings          Company    5
15  Muthanna              Fname      6
16  Shareef               Lname      6
17  GFTC                  Company    6

我需要能够使用 php mysql 在 HTML table 中呈现数据

First Name       Last Name       Company

Ankur            Gupta           ASS Holdings
Christie         Trojillo        AWS

而且我还需要能够按公司对 table 进行排序。

这是我尝试做的，但我知道这是完全错误的，因为数据库可能只有 Fname 和 Lname 而没有公司，这将导致转义并使用下一个值并破坏 table 和数据也可以以不同的顺序存储

$sql="SELECT * FROM system_frm_item_metas ORDER BY item_id";
$result=mysqli_query($con,$sql);
if ($result->num_rows > 0) {

echo "<table><tr><th>First Name</th><th>Last Name</th><th>Company</th></tr>";
while($row = $result->fetch_assoc()) {
   if ($row["field_id"] == "Fname") { echo "<tr><td>".$row["meta_value"]."</td>";}
   if ($row["field_id"] == "Lname") { echo "<td>".$row["meta_value"]."</td>";}
   if ($row["field_id"] == "Company") { echo "<td>".$row["meta_value"]."</td></tr>";}     
}
echo "</table>";

非常感谢任何帮助

Answer 1

DROP TABLE IF EXISTS eav_hell;

CREATE TABLE eav_hell
(entity INT NOT NULL
,attribute VARCHAR(12) NOT NULL
,value VARCHAR(30) NOT NULL
,PRIMARY KEY(entity,attribute)
);

INSERT INTO eav_hell VALUES
(1 ,'Fname','Ankur'),
(1 ,'Lname','Gupta'),
(1 ,'Company','AAS Holdings'),
(2 ,'Fname','Christie'),
(2 ,'Lname','Trojillo'),
(2 ,'Company','AWS'),
(3 ,'Fname','Devadanam'),
(3 ,'Lname','Pulukuri'),
(3 ,'Company','AAS Holdings'),
(4 ,'Fname','Radha'),
(4 ,'Lname','Neupane'),
(5 ,'Fname','Marites'),
(5 ,'Lname','Torsar'),
(5 ,'Company','AAS Holdings'),
(6 ,'Fname','Muthanna'),
(6 ,'Lname','Shareef'),
(6 ,'Company','GFTC');

SELECT entity
     , MAX(CASE WHEN attribute = 'Fname' THEN value END) Fname
     , MAX(CASE WHEN attribute = 'Lname' THEN value END) Lname
     , MAX(CASE WHEN attribute = 'Company' THEN value END) Company
  FROM eav_hell
 GROUP
    BY entity;

+--------+-----------+----------+--------------+
| entity | Fname     | Lname    | Company      |
+--------+-----------+----------+--------------+
|      1 | Ankur     | Gupta    | AAS Holdings |
|      2 | Christie  | Trojillo | AWS          |
|      3 | Devadanam | Pulukuri | AAS Holdings |
|      4 | Radha     | Neupane  | NULL         |
|      5 | Marites   | Torsar   | AAS Holdings |
|      6 | Muthanna  | Shareef  | GFTC         |
+--------+-----------+----------+--------------+

或（更快但不够优雅）...

SELECT DISTINCT e.entity
              , f.value fname
              , l.value lname
              , c.value company
           FROM eav_hell e
           LEFT 
           JOIN eav_hell f
             ON f.entity = e.entity
            AND f.attribute = 'fname'
           LEFT 
           JOIN eav_hell l
             ON l.entity = e.entity
            AND l.attribute = 'lname'
           LEFT 
           JOIN eav_hell c
             ON c.entity = e.entity
            AND c.attribute = 'company';

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