我如何在T-SQL / Linq中查詢這個復雜的查詢？

Question

目前我有2張桌子

[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

如何在每個CAT_PARENT中選擇具有多個子類別的前15個帖子行。 因此，CAT_PARENT及其所有孩子的總帖子數僅為15.我們這里有多個CAT_PARENT。 所以我們可以為每個CAT_PARENT及其子類別返回多個帖子，其中包含15個帖子

這里的問題是讓它在一次查詢SQL服務器中，因為一個查詢最多可能需要200個帖子，所以如果你可以在1個T-sQL查詢/ linq查詢中編寫它，它可能是最好的。

如果你能用LINQ寫它，我更喜歡。 但是在T-SQL中編寫它也是可以的。

非常感謝你 ：）

---

感謝Alexander的解決方案在這里，我修改了一些部分，它可以很好地使用186查詢和一些延遲加載的列不到2秒（遠程）到我的SQL服務器

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，幫助查詢根據降序日期而不是ID升序選擇前15名

Answer 1

我不確定是否有任何方法可以使用linq執行此操作而不會提取超出必要的信息，但這里有一個T-SQL腳本可以完成任務。 為了確保我理解了這個要求，這里是我對腳本的描述：

此腳本從“類別”具有多於1個子類別的“帖子”表中選擇前15個條目：

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

Answer 2

如果是SQL Server 2005或更高版本，您可以執行以下操作：

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

這是我用於創建測試表的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());

Answer 3

我想像linq2sql這樣的東西：

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))