Question

I’m using SQL Server 2008, I want select random row record, and the total number of record is depend on another table’s column value, how to do this?

My SQL statement is something like this, but wrong..

select top b.number a.name, a.link_id 
from A a 
left join B b on b.link_id = a.link_id 
order by newid()

Here are my tables and the expected result.

Table A:

name   link_id 
james  100
albert 100
susan  100
simon  101
tom    101    
fion   101

Table B:

link_id   number
100       2
101       1

Expected result:

• when run 1st time, result may be:

  name   link_id
  james  100
  susan  100
  fion   101
  

• 2nd time result may be:

  albert 100
  susan  100
  simon  101
  

• 3rd time could be:

  james  100
  albert 100
  fion   101
  

Explaination

Refer to table B, link_id: 100, number: 2

meaning that Table A should select out 2 random record for link_id = 100

and need to select 1 random record for link_id=101

Answer 1

You can use the ROW_NUMBER() function:

SELECT A.name, A.link_id
FROM(
SELECT name,link_id, ROW_NUMBER()OVER(PARTITION BY link_id ORDER BY NEWID()) rn
FROM dbo.tblA
) AS A
JOIN dbo.tblB AS B
ON A.link_id = B.link_id
WHERE A.rn <= B.number;

Here is a SqlFiddle to show this in action: http://sqlfiddle.com/#!3/92eac/2