MySQL：多行结果与单行结果

Question

I have these three tables,

page table

page_id    page_title
1          a

content table

content_id   content_text
1            text one
2            text two

content structure table

page_id     content_id     order_in_page
1           1              1
1           2              2

my working sql,

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.page_url = 'a'

result,

page_id   page_title   content_text    order_in_page
1         a            text one        1    
1         a            text two        2

the result I am after

page_id   page_title   content_1   content_2    content_3    content_4
1         a            text one    text two     null         null

How can I make the multi-row result into a single row result?

Or maybe the multi rows result is better and faster than a single row result that I want?

EDIT:

the reason I want a single row result is that I can just call the content_# by doing this,

echo $page['content_1'];

just like I call the title,

echo $page['page_title'];

Answer 1

Again, your thinking is in the wrong spot, this, if it is possible to do, would be discouraged, inefficient and probably is not possible.

Instead, handle the data in the loop and do with it what you want there, it may seem like it is more inefficient in the loop, but I assure it is not.

foreach ($dataFromSQL as $data) {
    $page[] = $data;
}

// Later on when you want to access it:
echo $page[0]['page_title'];
echo $page[0]['content_text'];

Where 0 would be the first row, 1 would be the second etc.

Answer 2

You can do this quite easily using GROUP BY with an IF statement for each column you want to transpose. When MAX evaluates it will always evaluate a non-null value as greater than NULL.

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.page_url = 'a'
GROUP BY page_id