sql server 查询表某个字段不重复数据

SELECT TOP (500) ID, Personname, Personcode, Telphone, Fraction
into temp3
FROM Records AS a
WHERE (LEN(Personcode) = 18 OR
      LEN(Personcode) = 15) AND (NOT EXISTS
          (SELECT 1 AS Expr1
         FROM Records
         WHERE (Personname = a.Personname) AND (Fraction > a.Fraction) OR
               (Personname = a.Personname) AND (Fraction = a.Fraction) AND (ID < a.ID)))
ORDER BY Fraction DESC