WITH scores (score)
     AS
     (
      SELECT CAST(score AS INTEGER)
        FROM (
              VALUES (0),(10),(10)
             ) AS scores (score)
     )
SELECT AVG(CAST(score AS DECIMAL(19,8))) AS precision_eight,AVG(CAST(score AS DECIMAL(19,7))) AS precision_seven,6))) AS precision_six,5))) AS precision_five,4))) AS precision_four
  FROM scores;

结果：

precision_eight | precision_seven | precision_six | precision_five | precision_four 
     6.66666666 |       6.6666666 |      6.666666 |       6.666666 |       6.666666

为什么我总是得到至少六位小数？这是记录在案的行为？

(我正在运行sql Server 2008)