mysql - 将两部分 SQL 查询合并为一个查询

Question

这就是我所拥有的：

询问

select
bc.short_desc as cdesc
from
blog_post as bp 
left join blog_post_category_link as blpc on bp.post_id = blpc.post_id
inner join blog_category as bc on blpc.cat_id = bc.cat_id
where bp.post_id = 1

结果

----------------
| |cdesc       |
----------------
|1|Top level   |
----------------
|2|Sub level   |
----------------
|3|SubSub level|
----------------

第二次查询

select
bt.short_desc as tdesc
from
blog_post as bp 
left join blog_post_tag_link as blpt on bp.post_id = blpt.post_id
inner join blog_tag as bt on blpt.tag_id = bt.tag_id
where bp.post_id = 1

第二个结果

----------------
| |tdesc       |
----------------
|1|Tag1        |
----------------
|2|Tag2        |
----------------

加入这两个查询后的期望结果

----------------------
| |cdesc       |tdesc|
----------------------
|1|Top level   |Tag1 |
----------------------
|2|Sub level   |Tag2 |
----------------------
|3|SubSub level|     |
----------------------

有可能吗？

Answer 1

试试这个查询

SET @rn1 = 0;
SET @rn2 = 0;

SELECT t1.rId, t1.cdesc, t2.tdesc
FROM 
(select @rn1 := rn1 + 1 AS rId, bc.short_desc as cdesc
from blog_post as bp 
left join blog_post_category_link as blpc on bp.post_id = blpc.post_id
inner join blog_category as bc on blpc.cat_id = bc.cat_id
where bp.post_id = 1) t1, 
(select @rn2 := rn2 + 1 AS rId, bt.short_desc as tdesc
from blog_post as bp 
left join blog_post_tag_link as blpt on bp.post_id = blpt.post_id
inner join blog_tag as bt on blpt.tag_id = bt.tag_id
where bp.post_id = 1) t2
WHERE t1.rId = t2.rId;

对于 MS SQL 服务器

SELECT t1.rId, t1.cdesc, t2.tdesc
FROM 
(select row_number() over(order by bp.post_id) AS rId, bc.short_desc as cdesc
from blog_post as bp 
left join blog_post_category_link as blpc on bp.post_id = blpc.post_id
inner join blog_category as bc on blpc.cat_id = bc.cat_id
where bp.post_id = 1) t1, 
(select row_number() over(order by bp.post_id) AS rId, bt.short_desc as tdesc
from blog_post as bp 
left join blog_post_tag_link as blpt on bp.post_id = blpt.post_id
inner join blog_tag as bt on blpt.tag_id = bt.tag_id
where bp.post_id = 1) t2
WHERE t1.rId = t2.rId;

Answer 2

使用此模板，只需将上面的查询作为 T1 和 T2 的子查询插入：

Select *
from ( 
) T1 
join ( 
) T2  on T2.tdesc = T1.cdesc and T2.Tag1 = T1.TopLevel and T2.Tag2 = T1.SubLevel

Answer 3

SELECT
bc.short_desc AS cdesc, bt.short_desc AS tdesc
FROM
blog_post AS bp
LEFT JOIN blog_post_category_link AS blpc ON bp.post_id = blpc.post_id
INNER JOIN blog_category AS bc ON blpc.cat_id = bc.cat_id
LEFT JOIN blog_post_tag_link AS blpt ON bp.post_id = blpt.post_id
INNER JOIN blog_tag AS bt ON blpt.tag_id = bt.tag_id
WHERE bp.post_id = 1