crackman base 53 retain是非执行语句是什么意思啊

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如题，没有理解retain是非执行语句。求指导~


54.Consider the following data step:

data WORK.TEST;
    set SASHELP.CLASS(obs=5);
    retain City \’Beverly Hills\';
    State=\’California\';
run;

The computed variables City and State have their values assigned using two different methods, a RETAIN statement and an Assignment statement. Which statement regarding this program is true?
    A. The RETAIN statement is fine, but the value of City will be truncated to 8
bytes as the LENGTH statement has been omitted.
     B. Both the RETAIN and assignment statement are being used to initialize new
variables and are equally efficient. Method used is a matter of programmer preference.
     C. The assignment statement is fine, but the value of City will be truncated
to 8 bytes as the LENGTH statement has been omitted.
     D. City\’s value will be assigned one time, State\’s value 5 times.
Answer: D

其实这里考察的RETAIN到底是在非执行语句还是执行语句。
RETAIN的作用是初始化变量为“特定的默认值”，是非执行语句，在编译过程中，PDV中用“特定的默认值”替代SAS系统默认值。在DATA步中，加入STATE进入PDV中，STATE=\’California\'; 是赋值语句，也就是执行语句。每一次从SASHELP.CLASS读取数据之后，都要执行一次赋值语句。

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