复杂的求和问题!!

Question

oracle9i数据库,通过pl/sql操作,现有一表WW,有K,a,b,c,d五个字段,3000到4000左右条记录,欲求甲,乙2个结果,要对所有记录执行如下操作：
如果K=1,
    一:若(a-b)-c>=0,甲=b,乙=c;
    二:若(a-b)-c<0,甲=b,乙=a-b;
如果K=0,
    一:若(a-b)-d>=0,甲=b+d,乙=0;
    二:若(a-b)-d<0,甲=a,乙=0;最后，对甲和乙的结果分别累加，输出甲和乙的结果，具体的SQL语句该怎么写呢？？

Answer 1

SELECT SUM (DECODE (k, 1, b, CASE
                       WHEN (a - b) - d >= 0
                          THEN b + d
                       ELSE a
                    END)) 甲合计,
       SUM (DECODE (k, 0, 0, CASE
                       WHEN (a - b) - c >= 0
                          THEN c
                       ELSE a - v
                    END)) 乙合计
  FROM ww

Answer 2

select sum(甲) , sum(乙) 乙
  from (select case
                 when k = 1 then
                  b
                 when (k = 0 and a - b - d > 0) then
                  b + d
                 when (k = 0 and a - b - d < 0) then
                  a
               end 甲 ,
               case
                 when k = 0 then
                  0
                 when (k = 1 and a - b - c > 0) then
                  c
                 when (k = 1 and a - b - c < 0) then
                  a - b
               end 乙
          from ww)

Answer 3

如果现在还想求sum(a)的值呢??sum(a)只要直接求就可以了不要加这些判断条件,
也就是说,输出的结果是sum(甲),sum(乙),sum(a),恳求具体的SQL语句,不胜感激!!

Answer 4

SELECT sum(yi),SUM(jia) FROM
(
SELECT k,decode(k,1,decode(sign((a-b)-c),-1,a-b,c),
                0,0) yi FROM ww) a,
(               
SELECT k,decode(k,1,b,
                0,decode(sign((a-b)-d),-1,a,b + d)) jia FROM ww )b 
WHERE a.k = b.k