查看数据透视表中的数据（垂直mysql表）

Question

I'm really confused with pivot tables, please see what I have and what I need to achieve:

This is my mysql table structure

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

I need to be able to present the data in HTML table using php mysql in that way

First Name       Last Name       Company

Ankur            Gupta           ASS Holdings
Christie         Trojillo        AWS

And I also need to be able to sort that table by Company for example.

Here is what I tried to do but I know its totally wrong because the database could have only the Fname and Lname without the company which will cause to escape and use the next value and break the table and also the data could be stored in different order

$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>";

Any help will be really appreciated

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         |
+--------+-----------+----------+--------------+

or (faster but less elegant)...

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';