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如何在T-SQL/LINQ中查询这个复杂的查询?

tsql linq-to-sql c#

DucDigital · 技术社区 · 14 年前

目前我有两张桌子

[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

如何在每个有多个子类别的cat_父级中选择前15行文章。所以在猫咪家长和它的所有孩子的职位总数只有15个。我们这里有多个猫的父母。所以我们可以返回多组post,每个cat_父类和子类包含15个post

这里的问题是在一次到SQL Server的查询循环中使用它,因为一个查询最多可以占用200个日志,所以如果您可以在1个T-SQL查询/LINQ查询中编写它,那么它可能是最好的。

我希望你能用linq写。但用T-SQL编写也可以。

非常感谢:)

多亏了下面的Alexander解决方案,我修改了一些部分,它可以很好地处理186个查询和一些延迟加载的列(远程地)到我的SQL Server。

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个

3 回复 | 直到 14 年前

Alex Shirshov 14 年前

如果是用于SQL Server 2005或更高版本,则可以执行以下操作:

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

下面是我用来创建测试表的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());

Jake 14 年前

我不确定是否有任何方法可以在不提取超出必要的信息的情况下使用LINQ来完成这项任务,但是这里有一个T-SQL脚本可以完成这项任务。为了确保我理解需求,下面是我对脚本的描述:

此脚本从“日志”表中选择前15个条目,该表的类别包含多个子类别:

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

Francisco 14 年前

我想Linq2sql应该是这样的:

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))