ORACLE，DECODE函数和排名函数DENSE_RANK函数的使用

这几天写一个报表的页面，从很恶心的数据结构中做一个聚合函数的查询，结构大概是这个样子的：

所以有：对数据group by t.id,t.name.t.course

这样三层排序，然后用函数去取值。

• decode（feildname,'Match_value','value1','value2'）   -- 用字段名称去跟Match_value做对比，对比成功，返回value1  否则返回 value1 

这里把decode（）放在group by 的select内部，同聚合函数一起使用，计算对应值。

很明显，这里得到的数据结构并不是我想要的样子，但是以目前水平暂时只能做到这里了。后边的放在js里处理的。

• 排名函数：dense_rank

这个用法其实也没太搞明白，应该是将数据集根据条件排序，但是存在排序的排名方式，这个dense_rank还有rank()和row_number()三个函数不同之处见：http://blog.csdn.net/winer2008/article/details/4283539

下边贴上测试用的所有代码：

• 表的创建修改，插入数据。

 create table KECHENG
 (
   id       NUMBER,
   name     VARCHAR2(20),
   course   VARCHAR2(20),
   score    NUMBER,
   examtime DATE,
   test1    VARCHAR2(50)
 )
 tablespace THRONESPACE
   pctfree 10
   initrans 1
   maxtrans 255
   storage
   (
     initial 64K
     next 1M
     minextents 1
     maxextents unlimited
   );

 insert into KECHENG (id, name, course, score, examtime, test1)
 values (1, '张三', '语文', 657, to_date('12-07-2017 05:00:00', 'dd-mm-yyyy hh24:mi:ss'), '');
 insert into KECHENG (id, name, course, score, examtime, test1)
 values (2, '张三', '数学', 476, to_date('11-07-2017 00:07:00', 'dd-mm-yyyy hh24:mi:ss'), '22ddd');
 insert into KECHENG (id, name, course, score, examtime, test1)
 values (2, '张三', '历史', 564, to_date('26-07-2017 04:00:00', 'dd-mm-yyyy hh24:mi:ss'), '');
 insert into KECHENG (id, name, course, score, examtime, test1)
 values (2, '李四', '语文', 534, to_date('26-07-2017 19:02:00', 'dd-mm-yyyy hh24:mi:ss'), '');
 insert into KECHENG (id, name, course, score, examtime, test1)
 values (2, '李四', '数学', 81, to_date('26-07-2017 17:57:00', 'dd-mm-yyyy hh24:mi:ss'), '');
 insert into KECHENG (id, name, course, score, examtime, test1)
 values (2, '李四', '历史', 933, to_date('20-07-2017 03:57:00', 'dd-mm-yyyy hh24:mi:ss'), '');
 insert into KECHENG (id, name, course, score, examtime, test1)
 values (3, '王五', '语文', 264, to_date('23-07-2017 05:03:00', 'dd-mm-yyyy hh24:mi:ss'), '');
 insert into KECHENG (id, name, course, score, examtime, test1)
 values (3, '王五', '数学', 25, to_date('10-07-2017 03:00:00', 'dd-mm-yyyy hh24:mi:ss'), '');
 insert into KECHENG (id, name, course, score, examtime, test1)
 values (3, '王五', '历史', 45, to_date('03-07-2017 11:00:00', 'dd-mm-yyyy hh24:mi:ss'), '');
 insert into KECHENG (id, name, course, score, examtime, test1)
 values (2, '张三', '语文', 667, to_date('12-07-2017 05:00:00', 'dd-mm-yyyy hh24:mi:ss'), '');
 insert into KECHENG (id, name, course, score, examtime, test1)
 values (1, '张三', '数学', 766, to_date('11-07-2017 00:09:00', 'dd-mm-yyyy hh24:mi:ss'), '');
 insert into KECHENG (id, name, course, score, examtime, test1)
 values (2, '张三', '历史', 546, to_date('26-07-2017 04:03:00', 'dd-mm-yyyy hh24:mi:ss'), '');
 insert into KECHENG (id, name, course, score, examtime, test1)
 values (2, '李四', '语文', 54, to_date('26-07-2017 19:00:00', 'dd-mm-yyyy hh24:mi:ss'), '');
 insert into KECHENG (id, name, course, score, examtime, test1)
 values (1, '李四', '数学', 821, to_date('26-07-2017 17:00:00', 'dd-mm-yyyy hh24:mi:ss'), '');
 insert into KECHENG (id, name, course, score, examtime, test1)
 values (2, '李四', '历史', 93, to_date('20-07-2017 03:00:00', 'dd-mm-yyyy hh24:mi:ss'), '');
 insert into KECHENG (id, name, course, score, examtime, test1)
 values (3, '王五', '语文', 254, to_date('23-07-2017 05:00:00', 'dd-mm-yyyy hh24:mi:ss'), '');
 insert into KECHENG (id, name, course, score, examtime, test1)
 values (3, '王五', '数学', 245, to_date('10-07-2017 03:58:00', 'dd-mm-yyyy hh24:mi:ss'), '');
 insert into KECHENG (id, name, course, score, examtime, test1)
 values (3, '王五', '历史', 454, to_date('03-07-2017 10:00:00', 'dd-mm-yyyy hh24:mi:ss'), '');
 insert into KECHENG (id, name, course, score, examtime, test1)
 values (1, '张三', '语文', 677, to_date('12-07-2017 05:02:00', 'dd-mm-yyyy hh24:mi:ss'), '');
 insert into KECHENG (id, name, course, score, examtime, test1)
 values (1, '张三', '数学', 776, to_date('11-07-2017 00:07:00', 'dd-mm-yyyy hh24:mi:ss'), '');
 insert into KECHENG (id, name, course, score, examtime, test1)
 values (1, '张三', '历史', 56, to_date('26-07-2017 05:00:00', 'dd-mm-yyyy hh24:mi:ss'), '');
 insert into KECHENG (id, name, course, score, examtime, test1)
 values (2, '李四', '语文', 564, to_date('26-07-2017 21:00:00', 'dd-mm-yyyy hh24:mi:ss'), '');
 insert into KECHENG (id, name, course, score, examtime, test1)
 values (1, '李四', '数学', 481, to_date('26-07-2017 17:02:00', 'dd-mm-yyyy hh24:mi:ss'), '');
 insert into KECHENG (id, name, course, score, examtime, test1)
 values (1, '李四', '历史', 923, to_date('20-07-2017 03:00:00', 'dd-mm-yyyy hh24:mi:ss'), '');
 insert into KECHENG (id, name, course, score, examtime, test1)
 values (3, '王五', '语文', 24, to_date('23-07-2017 05:08:00', 'dd-mm-yyyy hh24:mi:ss'), '');
 insert into KECHENG (id, name, course, score, examtime, test1)
 values (3, '王五', '数学', 265, to_date('10-07-2017 03:02:00', 'dd-mm-yyyy hh24:mi:ss'), '');
 insert into KECHENG (id, name, course, score, examtime, test1)
 values (3, '王五', '历史', 465, to_date('03-07-2017 10:05:00', 'dd-mm-yyyy hh24:mi:ss'), '');
 insert into KECHENG (id, name, course, score, examtime, test1)
 values (1, '张三', '语文', 767, to_date('12-07-2017 07:00:00', 'dd-mm-yyyy hh24:mi:ss'), '');
 insert into KECHENG (id, name, course, score, examtime, test1)
 values (1, '张三', '数学', 276, to_date('11-07-2017 01:07:00', 'dd-mm-yyyy hh24:mi:ss'), '');
 insert into KECHENG (id, name, course, score, examtime, test1)
 values (1, '张三', '历史', 566, to_date('26-07-2017 04:00:00', 'dd-mm-yyyy hh24:mi:ss'), '');
 insert into KECHENG (id, name, course, score, examtime, test1)
 values (2, '李四', '语文', 454, to_date('26-07-2017 19:02:00', 'dd-mm-yyyy hh24:mi:ss'), '');
 insert into KECHENG (id, name, course, score, examtime, test1)
 values (2, '李四', '数学', 81, to_date('26-07-2017 17:00:00', 'dd-mm-yyyy hh24:mi:ss'), '');
 insert into KECHENG (id, name, course, score, examtime, test1)
 values (2, '李四', '历史', 953, to_date('20-07-2017 03:02:00', 'dd-mm-yyyy hh24:mi:ss'), '');
 insert into KECHENG (id, name, course, score, examtime, test1)
 values (1, '王五', '语文', 244, to_date('23-07-2017 05:00:00', 'dd-mm-yyyy hh24:mi:ss'), '');
 insert into KECHENG (id, name, course, score, examtime, test1)
 values (2, '王五', '数学', 425, to_date('10-07-2017 03:00:00', 'dd-mm-yyyy hh24:mi:ss'), '');
 insert into KECHENG (id, name, course, score, examtime, test1)
 values (3, '王五', '历史', 45, to_date('03-07-2017 10:02:00', 'dd-mm-yyyy hh24:mi:ss'), '');
 commit;

• 查询用的sql

 select t.id,
        t.name,
        t.course,
        max(decode(t.course, '语文', score, 0)) yuwenmax,
        min(decode(t.course, '语文', score, 0)),
        round(avg(decode(t.course, '语文', score, 0)), 4),
        max(decode(t.course, '历史', score, 0)),
        min(decode(t.course, '历史', score, 0)),
        round(avg(decode(t.course, '历史', score, 0)), 4),
        max(decode(t.course, '数学', score, 0)),
        min(decode(t.course, '数学', score, 0)),
        round(avg(decode(t.course, '数学', score, 0)), 4),
        decode(t.course,
               '数学' ，min(t.score) KEEP(dense_rank first ORDER BY t.examtime),
               0)  as start_value,                                                                     --这里取起始值，结束值和增量
        decode(t.course,
               '数学' ，min(t.score) KEEP(dense_rank last ORDER BY t.examtime),
               0) as end_value,
        decode(t.course,
               '数学' ，min(t.score) KEEP(dense_rank last ORDER BY t.examtime),
               0) -
        decode(t.course,
               '数学' ，min(t.score) KEEP(dense_rank first ORDER BY t.examtime),
               0) as minus_value
   from kecheng t
  group by t.id, t.name, t.course
  order by t.id,
           t.name