求查询处置

求查询处理
想完成一个统计,一个表是这样的:
年月                    单位               分类1                  分类2
201401             1001                    A                      C
201401             1001                    B                      D
201401             1002                    B                      D
201401             1002                    A                      D
201401             1002                    B                      C
201402             1001                    A                      C
201402             1001                    B                      D
201402             1002                    B                      D
201402             1002                    A                      D
201402             1002                    B                      C
现在想分单位,分年月统计成如下表:
年月      单位          分类1-A条数        分类1-B条数        分类2-C条数     分类2-D条数

怎么处理
谢谢!
------解决方案--------------------
SELECT  年月,单位,
SUM(DECODE(分类1,'A',1)) "分类1-A条数",
SUM(DECODE(分类1,'B',1)) "分类1-B条数",
SUM(DECODE(分类2,'C',1)) "分类2-C条数",
SUM(DECODE(分类2,'D',1)) "分类2-D条数"
FROM T
GROUP BY 年月,单位
ORDER BY 年月,单位