算法问题:用SQL写出当M*N时的螺旋矩阵算法

　　以下是一个4*4的矩阵:

　　1 12 11 10

　　2 13 16 9

　　3 14 15 8

　　4 5 6 7

　　请照上面矩阵的规律, 用SQL写出当M*N时的矩阵算法。

　　实现的sql与效果: 　

　　代码:---------------------------------------------

　　SQL> -- 逆时针的

　　SQL> select --i,

　　 2 sum(decode(j, 1, rn)) as co11,

　　 3 sum(decode(j, 2, rn)) as co12,

　　 4 sum(decode(j, 3, rn)) as co13,

　　 5 sum(decode(j, 4, rn)) as co14

　　 6 from (select i, j, rank() over(order by tag) as rn

　　 7 from (select i,

　　 8 j,

　　 9 -- 逆时针螺旋特征码 counter-clockwise

　　 10 case least(j - 1, 4 - i, 4 - j, i - 1)

　　 11 when j - 1 then

　　 12 (j - 1) || "1" || i

　　 13 when 4-i then

　　 14 (4 - i) || "2" || j

　　 15 when 4 - j then

　　 16 (4 - j) || "3" || (4 - i)

　　 17 when i - 1 then

　　 18 (i - 1) || "4" || (4 - j)

　　 19 end as tag

　　 20 from (select level as i from dual connect by level <= 4) a,

　　 21 (select level as j from dual connect by level <= 4) b))

　　 22 group by i

　　 23 /

　　 CO11 CO12 CO13 CO14

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