STR
--------------------------------------------------------------------------------------------

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SQL>--------------------------------------------------------------------------------
使用前, 给声明m和n并赋值

代码:--------------------------------------------------------------------------------
var n number;
var m number;

exec :n := &n; :m=&m;

with t as (
  select :n as n, :m as m from dual
)
select replace(max(sys_connect_by_path(rank, '''','''')), '''','''') str
  from (select i, j, to_char(rank() over(order by tag), ''''999999'''') as rank
          from (select i,
                       j,
                       -- 顺时针螺旋特征码 clockwise
                       case least(i - 1, m - j, n - i, j - 1)
                         when i - 1 then
                          to_char(i - 1, ''''fm0000'''') || ''''1'''' ||
                          to_char(j - 1, ''''fm0000'''')
                         when m - j then
                          to_char(m - j, ''''fm0000'''') || ''''2'''' ||
                          to_char(i - 1, ''''fm0000'''')
                         when n - i then
                          to_char(n - i, ''''fm0000'''') || ''''3'''' ||
                          to_char(m - j, ''''fm0000'''')
                         when j - 1 then
                          to_char(j - 1, ''''fm0000'''') || ''''4'''' ||
                          to_char(n - i, ''''fm0000'''')
                       end as tag
                  from (select n, level as i from t connect by level <= n) a,
                       (select m, level as j from t connect by level <= m) b))
 start with j = 1
connect by j - 1 = prior j and i = prior i
 group by i
-----------------------------------------------------------------------------------------------

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