select name,
       to_char(min(ny), 'yyyymm') || '--' || to_char(max(ny), 'yyyymm'),
       danwei
  from (select name, ny, to_char(ny, 'yyyymm') - rownum rn, danwei from t order by name,danwei,ny)
 where name = '张三'
 group by rn, name, danwei
 order by 2;

------解决方案--------------------
SQL code

WITH t AS
(
  SELECT '张三' name, to_date('200001','YYYYMM') ny,'一队' danwei FROM dual UNION ALL
  SELECT '张三' name, to_date('200201','YYYYMM') ny,'一队' danwei FROM dual UNION ALL
  SELECT '张三' name, to_date('200202','YYYYMM') ny,'二队' danwei FROM dual UNION ALL
  SELECT '张三' name, to_date('200301','YYYYMM') ny,'二队' danwei FROM dual UNION ALL
  SELECT '张三' name, to_date('200302','YYYYMM') ny,'三队' danwei FROM dual UNION ALL
  SELECT '李四' name, to_date('200001','YYYYMM') ny,'一队' danwei FROM dual
     )


select a.name,
       to_char(a.ny,'YYYYMM') || '--' || to_char(b.ny,'YYYYMM') ny,
       a.danwei
  from 
       (select name, min(ny) ny, danwei from t GROUP BY NAME,danwei) a
      LEFT JOIN 
           (select name, MAX(ny) ny, danwei from t GROUP BY NAME,danwei) b 
            ON a.name = b.name AND a.danwei = b.danwei
 group by a.name ,to_char(a.ny,'YYYYMM') || '--' || to_char(b.ny,'YYYYMM') ,a.danwei
 order by 1,2,3;