SQLSERVER判断是否为数字ISNUMERIC

从SQLSERVER 2005新增isnumeric函数，返回1则字符串是数值，返回0则认为不是数值

但里面有些其他的字符也返回1，不知道是怎么个思路，是不是花旗国的规则？

SELECT ISNUMERIC ('123.456') AS '123.456', --1
       ISNUMERIC ('-') AS '-',  -- 1
       ISNUMERIC ('+') AS '+',  -- 1
       ISNUMERIC ('$') AS '$',  -- 1
       ISNUMERIC ('.') AS '.',  -- 1
       ISNUMERIC (',') AS ',',  -- 1
       ISNUMERIC ('\') AS '\',  -- 1
       ISNUMERIC ('1D1') AS '1D1',  -- 1
       ISNUMERIC ('1E1') AS '1E1',  -- 1
       ISNUMERIC ('1d1') AS '1d1',  -- 1
       ISNUMERIC ('1e1') AS '1e1',  -- 1
       ISNUMERIC ('d') AS 'd',  -- 0
       ISNUMERIC ('e') AS 'e'  -- 0