使用子查询。

SELECT r.nID,
(SELECT r1.val FROM T1 r1 WHERE r.nID=r1.nID ORDER BY rand() LIMIT 1) AS 'val' FROM T1 r 
GROUP BY r.nID

http://sqlfiddle.com/#!2/357b8/18

您可以使用兰德（）排序，然后按它们分组。
喜欢

SELECT nID, VAL FROM (
  SELECT nID, VAL
  FROM T1
  ORDER BY RAND()
  )AS subquery
GROUP BY nID

SELECT 
  t1.nID, 
  (SELECT 
     t2.var 
   FROM your_table t2 
   WHERE t1.nID = t2.nID ORDER BY rand() LIMIT 1
  ) AS var 
FROM your_table t1 
GROUP BY t1.nID ;

试试这个

SELECT nID, VAL
FROM (select nID, VAL from T1 order by rand()) as T
group by nID

下面的解决方案在本质上与xdazz或jonnyynnoj中的解决方案类似，但我使用子查询来选择所有不同的ID，而不是SELECT FROM T1 GROUP BY nID。我相信性能可能会有所不同，所以给予这个解决方案。

SELECT nID,
  (SELECT VAL
   FROM T1
   WHERE T1.nID = ids.nID
   ORDER BY RAND()
   LIMIT 1
  ) AS VAL
FROM (SELECT DISTINCT nID FROM T1) AS ids

兰德+行编号

SELECT t.*
, @rownum := @rownum+1 AS rowNum
FROM(
  SELECT nID, VAL 
  FROM T1 
  ORDER BY RAND()
) AS t, (SELECT @rownum :=0) AS R
GROUP BY nID
ORDER BY nID, rowNum