如何為每個主鍵打印與其相關的所有外鍵列？

Question

我想解決 PHP 問題

1. 我有一個帶有 2 個表的數據庫：第一個是“文檔”：

    id | title | ================================ 1 | equations | 2 | great | 3 | painting |

第二個是“圖片”：

          id   |   doc_id        |   description
    ===============================================
           1   |    1            |  "mathematics"
           2   |    1            |  "physic"
           3   |    2            |  "literature"
           4   |    2            |  "art"
     

2. "doc_id" 是一個外鍵，與表 "document" 的 id 相關

3. 這是我的問題：我正在嘗試為每個標題打印與之相關的所有描述，例如：

    for the title "equations", the foreign key related to it, is "doc_id =1" which means for "equations" I will print "mathematics" and "physic"

在我的瀏覽器上使用 PHP 和 SQL 打印的最終表格應該是：

             |   title       |   description
    ===============================================
             | equations     |  mathematics, physic
             | great         |   literature , art 
             | painting      |  
        

這是我的代碼：

<?php
$servername = "localhost";
$username = "root";
$password = "root";
$dbname = "doc-pic";
// Create connection
$conn =  mysqli_connect($servername, $username, $password, $dbname);
// Check connection
$sql = "SELECT * FROM pic LEFT JOIN document ON pic.doc_id=document.id";
                   $result = mysqli_query($conn, $sql);
$sql1 = "SELECT title from document";
                  $result1 = mysqli_query($conn, $sql1);
?>
           <table>    
           <?php
 if (mysqli_num_rows($result1) > 0)
            while($row = mysqli_fetch_array($result1)){?>
            <tr>
            <td><?php echo $row["title"]; ?></td>
            </tr>
            <?php  if (mysqli_num_rows($result) > 0 )
                     while($row = mysqli_fetch_array($result)){
                     ?>
                     <tr>
                     <td><?php echo $row["doc_id"]; ?></td>
                     <td><?php echo $row["description"]; ?></td>
                     </td>
                     </tr>
                     </td>
           <?php }

 } ?>

Answer 1

使用left join和聚合：

select d.*,
       group_concat(p.description order by p.id) as full_description
from documents d left join
     pic p
     on p.doc_id = d.id
group by d.id;

請注意，這使用group by d.id以及select d.* 。 這是有效的，因為d.id是（大概） documents的主鍵。