假设我有一个数据库(shops)里面有nclassid(小类id),anclassid(大类id) 
数据如下: 
    nclassid               anclassid 
          625                       63 
          626                       63 
          625                       63 
          626                       63 

问题关键: 
            我想将anclassid(63)对应的nclassid(625,626)只筛选各一条记录出来. 
            请问sql语句怎样高效率地表示出来呢?谢谢各位!