Created by Wang, Jerry, last modified on May 10, 2017
struct2 = CORRESPONDING #( struct1 ).
col2 and col3 of structure 2 will be overwritten by fields from structur1
可以看到虽然structu2的COL4不相关，但是也变空了。
解决方法就是
struct2 = CORRESPONDING #( BASE ( base ) struct1 ).