有一种情形是：
可能是input变量类型及长度不合适，
可以查看log窗口显示的导入数据变量的类型和长度是否与原数据库中变量的相一致，
如果类型或者长度不一致，
就会出现缺失值的情况.

似乎是这样，那更改数据长度的命令是什么呢。。。

也有可能是数据混有character和numeric的数据，需要在import的时候加上mixed=yes;
sas网站上的解释是：

MIXED=YES|NO
specifies whether to convert numeric data values into character data values for a column of mixed data types. This option is valid only when importing (reading) data from Excel. The Microsoft Ace and Jet Excel engines handle this option.

YES
assigns a SAS character type for the column and converts all numeric data values to character data values when mixed data types are found. When you specify MIXED=YES, the connection is set in import mode and no updates are allowed.

NO
assigns numeric or character type for the column, depending on the majority of the type data that is found. Both numeric data in a character column and character data in a numeric column are imported as missing values.

可以类似这样
data temp;
infile 'XXX’  delimiter='XX' missover dsd;
informat var1 $10.;
informat var2 20.;
input var1 $ var2;
run;

查看log窗口显示的导入数据变量的类型和长度是否与原数据库中变量的相一致
不太明白
可以查看help中的informat语句后面的选项‘length’的详细解释...