通过SQL查询随机获取N行，这将与不同部分中的行总数成比例
我有一张表格，上面有很多问题，每个问题都属于一个部分：通过SQL查询随机获取N行，这将与不同部分中的行总数成比例,sql,sql-server,Sql,Sql Server,我有一张表格，上面有很多问题，每个问题都属于一个部分： Id Question SectionId 1 What is ... 3 2 Who is... 3 3 When is... 2 4 Why is... 1 5 How is... 3 大约有1000个问题，大约50个部分。但是，我的查询很简单，例如，我从特定部分的表中选择给定数量的问题 SELEC
Id Question SectionId
1 What is ... 3
2 Who is... 3
3 When is... 2
4 Why is... 1
5 How is... 3
SELECT TOP 10 [Id], [Question] FROM [Questions]
WHERE [SectionId] IN (1,2)
ORDER BY NEWID()
注意：SQL查询或EF Linq查询可以工作。我想不出一种方法可以在一个步骤中完成这项工作，除非您事先知道每个部分的数量和比例 如果必须在查询时计算这些值，则需要运行一个查询以获取部分和比例，并使用该部分和比例构建动态SQL查询 使用GROUP BY查询获取各部分ID和每个部分中的问题数，并按要包含的部分进行筛选 迭代该结果以构建一个动态的UNION ALL查询，该查询获取一个前n，根据每个部分的部分计数/问题总数的百分比计算n，每个部分一个查询，这样您就可以动态构建如下内容：
SELECT TOP 5 ID, Question --because SectionID 1 is 50% of the questions
FROM Questions
WHERE SectionID=1
ORDER BY NEWID()
UNION ALL
SELECT TOP 3 ID, Question --because SectionID 2 is 30% of the questions
FROM Questions
WHERE SectionID=2
ORDER BY NEWID()
UNION ALL
SELECT TOP 2 ID, Question --because SectionID 3 is 20% of the questions
FROM Questions
WHERE SectionID=3
ORDER BY NEWID()
然后通过这个人工列对查询结果进行排序。我想不出一种方法可以在一个步骤中完成这项工作，除非您事先知道每个部分的数量和比例 如果必须在查询时计算这些值，则需要运行一个查询以获取部分和比例，并使用该部分和比例构建动态SQL查询 使用GROUP BY查询获取各部分ID和每个部分中的问题数，并按要包含的部分进行筛选 迭代该结果以构建一个动态的UNION ALL查询，该查询获取一个前n，根据每个部分的部分计数/问题总数的百分比计算n，每个部分一个查询，这样您就可以动态构建如下内容：
SELECT TOP 5 ID, Question --because SectionID 1 is 50% of the questions
FROM Questions
WHERE SectionID=1
ORDER BY NEWID()
UNION ALL
SELECT TOP 3 ID, Question --because SectionID 2 is 30% of the questions
FROM Questions
WHERE SectionID=2
ORDER BY NEWID()
UNION ALL
SELECT TOP 2 ID, Question --because SectionID 3 is 20% of the questions
FROM Questions
WHERE SectionID=3
ORDER BY NEWID()
然后按此人工列对查询结果进行排序。对于分层样本，在排序中进行第n个样本。这有点棘手，但应该可以：
SELECT TOP (10) q.*
FROM (SELECT q.*,
ROW_NUMBER() OVER (ORDER BY section, NEWID()) as seqnum,
COUNT(*) OVER (ORDER BY section, NEWID()) as cnt
FROM [Questions] q
WHERE [SectionId] IN (1, 2)
) q
ORDER BY seqnum % (cnt / 10);
这个逻辑可能有一些边界条件，但随着问题数量的增加和样本的足够大，它应该满足您的要求。对于分层样本，在排序上进行第n个样本。这有点棘手，但应该可以：
SELECT TOP (10) q.*
FROM (SELECT q.*,
ROW_NUMBER() OVER (ORDER BY section, NEWID()) as seqnum,
COUNT(*) OVER (ORDER BY section, NEWID()) as cnt
FROM [Questions] q
WHERE [SectionId] IN (1, 2)
) q
ORDER BY seqnum % (cnt / 10);
此逻辑可能有一些边界条件，但随着问题数量的增加和样本的足够大，它应该可以满足您的要求。在没有样本数据的情况下，这是未经测试的，但是，类似的方法可能会起作用：
WITH CTE AS(
SELECT ID,
Question,
SectionID,
ROW_NUMBER() OVER (ORDER BY NEWID()) AS RN,
(COUNT(ID) OVER (PARTITION BY SectionID) / (COUNT(ID) OVER () *1.0)) *10 AS Perc
FROM YourTable
)
SELECT TOP 10
ID,
Question,
SectionID
FROM CTE
WHERE RN <= CEILING(Perc)
ORDER BY RN ASC;
在缺少样本数据的情况下，这是未经测试的，但是，类似的方法可能会起作用：
WITH CTE AS(
SELECT ID,
Question,
SectionID,
ROW_NUMBER() OVER (ORDER BY NEWID()) AS RN,
(COUNT(ID) OVER (PARTITION BY SectionID) / (COUNT(ID) OVER () *1.0)) *10 AS Perc
FROM YourTable
)
SELECT TOP 10
ID,
Question,
SectionID
FROM CTE
WHERE RN <= CEILING(Perc)
ORDER BY RN ASC;
您可以使用以下选项在任何部分中始终选择10%的记录：
SELECT TOP ( select CAST(( COUNT(*) * 0.1 ) AS INT )
FROM QUESTION WHERE SECTIONID IN ( 1,2)) * FROM QUESTION
WHERE [SectionId] IN (1,2)
ORDER BY NEWID()
您可以使用以下选项在任何部分中始终选择10%的记录：
SELECT TOP ( select CAST(( COUNT(*) * 0.1 ) AS INT )
FROM QUESTION WHERE SECTIONID IN ( 1,2)) * FROM QUESTION
WHERE [SectionId] IN (1,2)
ORDER BY NEWID()
另一种选择，例如…返回每个部分总行数的20%
DECLARE @percentage numeric(10,2)
SET @percentage = 0.20 --20% of total question for section
SELECT [SectionID],[ID],[Question]
FROM ( SELECT
[ID],
[Question],
[SectionID],
ROW_NUMBER() OVER(PARTITION BY SectionID ORDER BY NEWID()) [idx],
COUNT(1) OVER(PARTITION BY SectionID) * @percentage AS [Proportional]
FROM [Questions]) tbl
WHERE
(tbl.[SectionID] = 1 AND tbl.[idx] <= [Proportional])
OR (tbl.[SectionID] = 2 AND tbl.[idx] <= [Proportional])
OR (tbl.[SectionID] = 3 AND tbl.[idx] <= [Proportional])
另一种选择，例如…返回每个部分总行数的20%
DECLARE @percentage numeric(10,2)
SET @percentage = 0.20 --20% of total question for section
SELECT [SectionID],[ID],[Question]
FROM ( SELECT
[ID],
[Question],
[SectionID],
ROW_NUMBER() OVER(PARTITION BY SectionID ORDER BY NEWID()) [idx],
COUNT(1) OVER(PARTITION BY SectionID) * @percentage AS [Proportional]
FROM [Questions]) tbl
WHERE
(tbl.[SectionID] = 1 AND tbl.[idx] <= [Proportional])
OR (tbl.[SectionID] = 2 AND tbl.[idx] <= [Proportional])
OR (tbl.[SectionID] = 3 AND tbl.[idx] <= [Proportional])
SELECT TOP 10 [Id], [Question] FROM [Questions]
WHERE [SectionId] IN (1,2)
ORDER BY NEWID()
declare @limit int = 10;
;with data as (
SELECT NTILE(100) over (partition by sectionid ORDER BY NEWID() ) as Centile, [Id], [Question]
FROM [Questions]
WHERE [SectionId] IN (1,2)
)
select * from data where centile <= @limit
您可以使用NTIL100函数以及over子句分区来获得
SELECT TOP 10 [Id], [Question] FROM [Questions]
WHERE [SectionId] IN (1,2)
ORDER BY NEWID()
declare @limit int = 10;
;with data as (
SELECT NTILE(100) over (partition by sectionid ORDER BY NEWID() ) as Centile, [Id], [Question]
FROM [Questions]
WHERE [SectionId] IN (1,2)
)
select * from data where centile <= @limit