按照书中例子写了一段，但是运行不出来，请高手解惑，先谢了。代码如下：
data codecity;
input id $ address $ @@;
cards;
010 west 020 south 0537 middle
;
data citychange;
set codecity;
select (id);
where ('010') id='BJ';
where ('020') id='TJ';
otherwise id='QT';
end;
run;
proc print data=citychange;
run;
------------------------------------------------------------------
NOTE: The SAS System stopped processing this step because of errors.
WARNING: The data set WORK.CITYCHANGE may be incomplete.  When this step was stopped there were
         0 observations and 2 variables.
WARNING: Data set WORK.CITYCHANGE was not replaced because this step was stopped.
NOTE: DATA statement used (Total process time):
      real time           0.04 seconds
      cpu time            0.01 seconds

89   proc print data=citychange;
90   run;
NOTE: No observations in data set WORK.CITYCHANGE.
NOTE: PROCEDURE PRINT used (Total process time):
      real time           0.00 seconds
      cpu time            0.00 seconds