MySQL：用于多行结果的标准方法VS基于集合的方法

Question

Following up on this question , there is problem with the standard approach or a recursive approach in the case below.

For instance, I want to return the page with the same parent_id and some pages have multiple row contents ,

page table

page_id    page_title   parent_id
1          a            1
2          aa           1
3          ab           1
4          ac           1

content table

content_id   content_text
1            text one
2            text two
3            text one aa
4            text two aa
5            text one ab
6            text one ac

content structure table

page_id     content_id     order_in_page
1           1              1
1           2              2
2           3              1
2           4              2
3           5              1
4           6              1

The standard approach,

SELECT 
    p.*,
    c.*,
    x.*

FROM pages AS p

LEFT JOIN pages_structures AS x
ON x.page_id = p.page_id

LEFT JOIN  pages_contents AS c
ON c.content_id = x.content_id

WHERE p.parent_id = '1'
AND p.page_id  != '1'

result (it lists the row as 4 items),

page_id   page_title  parent_id   content_text    order_in_page
2         aa           1          text one aa        1    
2         aa           1          text two aa        2
3         ab           1          text one ab        1
4         ac           1          text one ac        1        

As you can notice that there are two rows with page_id 2 and one row for each 3 and 4 . How do you display the data into HTML with the standard approach like below (as suggested in one of the answer in the previous question )?

echo $page[0]['page_title'];
echo $page[0]['content_text'];

But with set-based one, I can do it with this,

SELECT
   page_id,
   page_title, 
   MAX(IF(order_in_page = 1, content_text, NULL)) AS content_1,
   MAX(IF(order_in_page = 2, content_text, NULL)) AS content_2,
   .
   .
   .
FROM 
   pages AS p LEFT JOIN 
   pages_structures AS x ON x.page_id = p.page_id LEFT JOIN  
   pages_contents AS c ON c.content_id = x.content_id
WHERE
   p.parent_id = '1'
AND
   p.page_id != '1'
GROUP BY page_id

in PHP,

foreach($items as $item)
{
    echo '<li><h3>'.$item['page_title'].'</h3>';
    echo '<p>'.$item['content_1'].'</p>';
    echo '<p>'.$item['content_2'].'</p></li>';
}

the HTML (it lists the row as 3 items which is correct),

<li>
   <h3>aa</h3>
   <p>text one aa</p>
   <p>text two aa</p>
</li>

<li>
   <h3>ab</h3>
   <p>text one ab</p>
   <p></p>
</li>

<li>
   <h3>ac</h3>
   <p>text one ac</p>
   <p></p>
</li>

Hope this makes sense!

Answer 1

使用标准方法，您只需在变量中跟踪当前页面，然后在页面更改时滚动到新的列表项。