[英]How do i query this complex query in T-SQL / Linq?
目前我有2张桌子
[Category] -> PK| CAT_ID -> CAT_PARENT (link to itself | if it's a top parent category then it's 0)
[Posts] -> PK | POST_ID -> FK | CAT_ID | CREATE_DATE
如何在每个CAT_PARENT中选择具有多个子类别的前15个帖子行。 因此,CAT_PARENT及其所有孩子的总帖子数仅为15.我们这里有多个CAT_PARENT。 所以我们可以为每个CAT_PARENT及其子类别返回多个帖子,其中包含15个帖子
这里的问题是让它在一次查询SQL服务器中,因为一个查询最多可能需要200个帖子,所以如果你可以在1个T-sQL查询/ linq查询中编写它,它可能是最好的。
如果你能用LINQ写它,我更喜欢。 但是在T-SQL中编写它也是可以的。
非常感谢你 :)
感谢Alexander的解决方案在这里,我修改了一些部分,它可以很好地使用186查询和一些延迟加载的列不到2秒(远程)到我的SQL服务器
ALTER procedure [dbo].[get_topParentPost] (
@quantity int
)
as
WITH t AS (
SELECT ROW_NUMBER() OVER (PARTITION BY top_level.CAT_ID ORDER BY p.CREATE_DATE DESC) AS row_num,
top_level.CAT_ID AS top_level_cat_id, child_category.CAT_ID AS category_id, p.POST_ID, p.CREATE_DATE, p.VALIDATE,
p.CAT_ID, p.DESCRIPTION, p.DRAF_OF, p.END_DATE, p.MOD_DATE, p.ON_HOMEPAGE, p.PUBLISH_DATE, p.[STATE], p.THUMB_ID, p.TITLE, p.[TYPE],
p.[VIEW]
FROM
(SELECT cat_id, 0 as cat_parent FROM Categories c WHERE CAT_PARRENT = 0) AS top_level
INNER JOIN Categories AS child_category
ON child_category.CAT_PARRENT = top_level.CAT_ID OR child_category.CAT_ID = top_level.CAT_ID
INNER JOIN Posts p
ON child_category.CAT_ID = p.CAT_ID AND p.VALIDATE = 1
)
SELECT * FROM t WHERE row_num <= @quantity
我修改了一些部分,帮助查询根据降序日期而不是ID升序选择前15名
我不确定是否有任何方法可以使用linq执行此操作而不会提取超出必要的信息,但这里有一个T-SQL脚本可以完成任务。 为了确保我理解了这个要求,这里是我对脚本的描述:
此脚本从“类别”具有多于1个子类别的“帖子”表中选择前15个条目:
declare @cat_id int
declare MULTIPLE_CHILDREN_CATEGORIES cursor for
(
select cat_id
from categories
group by cat_parent
having count(*) > 1
)
open MULTIPLE_CHILDREN_CATEGORIES
fetch next from MULTIPLE_CHILDREN_CATEGORIES into @cat_id
while @@fetch_status = 0
begin
select top 15 *
from posts
where cat_id = @cat_id
order by create_date desc
fetch next from MULTIPLE_CHILDREN_CATEGORIES into @cat_id
end
close MULTIPLE_CHILDREN_CATEGORIES
deallocate MULTIPLE_CHILDREN_CATEGORIES
如果是SQL Server 2005或更高版本,您可以执行以下操作:
SELECT t.top_level_cat_id, t.category_id, t.post_id, t.post_date
FROM (
SELECT ROW_NUMBER() OVER (PARTITION BY top_level.cat_id ORDER BY p.post_id) AS row_num,
top_level.cat_id AS top_level_cat_id,
child_category.cat_id AS category_id,
p.post_id,
p.post_date
FROM
Post p
INNER JOIN Category AS child_category
ON child_category.cat_id = p.cat_id
INNER JOIN Category AS top_level
ON top_level.cat_id = child_category.cat_parent
) AS t
WHERE t.row_num <= 15
这是我用于创建测试表的T-SQL:
CREATE TABLE Category (cat_id INT, cat_parent INT);
--top level
INSERT INTO Category VALUES(1, 0);
INSERT INTO Category VALUES(2, 0);
-- child categories
INSERT INTO Category VALUES(3, 1);
INSERT INTO Category VALUES(4, 1);
INSERT INTO Category VALUES(5, 2);
CREATE TABLE Post(post_id INT, cat_id INT, post_date DATETIME);
INSERT INTO Post VALUES(1, 3, GETDATE());
INSERT INTO Post VALUES(2, 3, GETDATE());
INSERT INTO Post VALUES(3, 3, GETDATE());
INSERT INTO Post VALUES(4, 3, GETDATE());
INSERT INTO Post VALUES(5, 3, GETDATE());
INSERT INTO Post VALUES(6, 3, GETDATE());
INSERT INTO Post VALUES(7, 3, GETDATE());
INSERT INTO Post VALUES(8, 3, GETDATE());
INSERT INTO Post VALUES(9, 3, GETDATE());
INSERT INTO Post VALUES(10, 3, GETDATE());
INSERT INTO Post VALUES(11, 3, GETDATE());
INSERT INTO Post VALUES(12, 3, GETDATE());
INSERT INTO Post VALUES(13, 3, GETDATE());
INSERT INTO Post VALUES(14, 3, GETDATE());
INSERT INTO Post VALUES(15, 3, GETDATE());
-- these records won't appear
INSERT INTO Post VALUES(16, 3, GETDATE());
INSERT INTO Post VALUES(17, 4, GETDATE());
INSERT INTO Post VALUES(18, 4, GETDATE());
INSERT INTO Post VALUES(19, 5, GETDATE());
INSERT INTO Post VALUES(20, 5, GETDATE());
我想像linq2sql这样的东西:
IEnumerable<IEnumerable<Post>> posts = db.Categorys
.Where(p=>p.CAT_PARENT == 0)
.Select(p=>p.Categorys
.SelectMany(q=>q.Posts)
.OrderByDescending(q=>q.CREATE_DATE)
.Take(15))
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