如题，我在sas中操作出现了如下错误：
第一种尝试：
proc sql;

delete

from peter.myworld

where _n_=7;
quit;



136  proc sql;
137      delete
138      from peter.myworld
139      where _n_=7;
ERROR: The following columns were not found in the contributing tables: _n_.
140  quit;
NOTE: The SAS System stopped processing this step because of errors.
NOTE: PROCEDURE SQL used (Total process time):
      real time           0.01 seconds
      cpu time            0.01 seconds


第二种尝试：
proc sql;

delete

from peter.myworld

where noobs=7;
quit;


141  proc sql;
142      delete
143      from peter.myworld
144      where noobs=7;
ERROR: The following columns were not found in the contributing tables: noobs.
145  quit;
NOTE: The SAS System stopped processing this step because of errors.
NOTE: PROCEDURE SQL used (Total process time):
      real time           0.00 seconds
      cpu time            0.00 seconds
还有一个小疑惑就是，sas怎么会说找不到columns？