获取页面块

Question

我有三个表格：页面，块和pages_blocks。

我的数据库架构看起来如下：

CREATE TABLE `blocks` (
    `id` smallint(6) NOT NULL AUTO_INCREMENT, 
    `name` char(40) NOT NULL, 
    `content` text NOT NULL 
    PRIMARY KEY (`id`) 
); 

CREATE TABLE `pages` (
    `id` int(11) NOT NULL AUTO_INCREMENT, 
    `title` char(100) NOT NULL, 
    `content` mediumtext NOT NULL 
    PRIMARY KEY (`id`) 
); 

CREATE TABLE `pages_blocks` (
    `page_id` int(11) DEFAULT NULL, 
    `block_id` smallint(6) DEFAULT NULL, 
    `location` enum('left','right') DEFAULT NULL, 
    `display_order` smallint(6) DEFAULT NULL 
); 

什么是完美的SQL代码获取“左”和“右”块特定网页？

非常感谢您的帮助。

Answer 1

一种方式将是两个联接搜索左，右：

select * 
from pages p 
left join 
     (
     select * 
     from pages_blocks pb 
     join blocks b 
     on  pb.block_id = b.id 
     where pb.location = 'left' 
     ) left_block 
on  left_block.page_id = p.id 
left join 
     (
     select * 
     from pages_blocks pb 
     join blocks b 
     on  pb.block_id = b.id 
     where pb.location = 'right' 
     ) right_block 
on  right_block.page_id = p.id 
where p.id = 42 

这有没有使用group by只返回一个排的优势。

编辑：如果可以有多个 “右” 和 “左” 的块，你可以查询所有块，如：

select pb.location 
,  pb.display_order 
,  b.name 
,  b.content 
from pages p 
join pages_blocks pb 
on  pb.page_id = p.id 
join blocks b 
on  pb.block_id = b.id 
where p.id = 42 
order by 
     pb.location 
,  pb.display_order 

Answer 2

你可以使用UNION：

select a.content 
from blocks a, pages_blocks b 
where a.id=b.block_id and b.page_id=123 and b.location='left' 
union 
select a.content 
from blocks a, pages_blocks b 
where a.id=b.block_id and b.page_id=123 and b.location='right'