ORACLE的分组统计之ROLLUP(一)

Oracle 9i以后，扩展了group by 的功能，能够满足大部分多维数据的分析统计功能，主要表现：

1. rollup,cube,grouping sets 扩展group by字句提供了丰富的多维分组统计功能；

2. 3个扩展分组函数：grouping,grouping_id,group_id提供扩展group by的辅助功能:提供区别结果行属于哪个分组级别，区分NULL值，建立有意义的报表，对汇总结果排序，过滤结果行等；

3.对扩展group by允许按重复列分组，组合列分组，连接分组等，另外，grouping sets可以接受cube,rollup操作作为参数。

ROLLUP

没有rollup的union all功能

SQL> select a.dname, b.job, sum(b.sal) sum_sal
from scott.dept a, scott.emp b
where a.deptno = b.deptno
group by a.dname, b.job
union all
select a.dname, NULL, sum(b.sa l) sum_sal
from scott.dept a, scott.emp b
where a.deptno = b.deptno
group by a.dnam e
union all
select null, null, sum(b.sal) sum_sal
from scott.dept a, scott.emp b wh ere a.deptno = b.deptno;

显示结果：

DNAME          JOB          SUM_SAL
-------------- --------- ----------
SALES          MANAGER         2850
SALES          CLERK            950
ACCOUNTING     MANAGER         2450
ACCOUNTING     PRESIDENT       5000
ACCOUNTING     CLERK           1300
SALES          SALESMAN        5600
RESEARCH       MANAGER         2975
RESEARCH       ANALYST         6000
RESEARCH       CLERK           1900
ACCOUNTING                     8750
RESEARCH                      10875

DNAME          JOB          SUM_SAL
-------------- --------- ----------
SALES                          9400
                              29025

已选择13行。

执行计划
----------------------------------------------------------
Plan hash value: 3113041979

--------------------------------------------------------------------------------
----------
| Id  | Operation                      | Name    | Rows  | Bytes | Cost (%CPU)|
Time     |
--------------------------------------------------------------------------------
----------
|   0 | SELECT STATEMENT               |         |    19 |   479 |    13  (70)|
00:00:01 |
|   1 |  UNION-ALL                     |         |       |       |            |
         |
|   2 |   HASH GROUP BY                |         |    14 |   392 |     5  (20)|
00:00:01 |
|   3 |    NESTED LOOPS                |         |    14 |   392 |     4   (0)|
00:00:01 |
|   4 |     TABLE ACCESS FULL          | EMP     |    14 |   210 |     3   (0)|
00:00:01 |
|   5 |     TABLE ACCESS BY INDEX ROWID| DEPT    |     1 |    13 |     1   (0)|
00:00:01 |
|*  6 |      INDEX UNIQUE SCAN         | PK_DEPT |     1 |       |     0   (0)|
00:00:01 |
|   7 |   HASH GROUP BY                |         |     4 |    80 |     5  (20)|
00:00:01 |
|   8 |    NESTED LOOPS                |         |    14 |   280 |     4   (0)|
00:00:01 |
|   9 |     TABLE ACCESS FULL          | EMP     |    14 |    98 |     3   (0)|
00:00:01 |
|  10 |     TABLE ACCESS BY INDEX ROWID| DEPT    |     1 |    13 |     1   (0)|
00:00:01 |
|* 11 |      INDEX UNIQUE SCAN         | PK_DEPT |     1 |       |     0   (0)|
00:00:01 |
|  12 |   SORT AGGREGATE               |         |     1 |     7 |            |
         |
|* 13 |    TABLE ACCESS FULL           | EMP     |    14 |    98 |     3   (0)|
00:00:01 |
--------------------------------------------------------------------------------
----------

Predicate Information (identified by operation id):
---------------------------------------------------

   6 - access("A"."DEPTNO"="B"."DEPTNO")
  11 - access("A"."DEPTNO"="B"."DEPTNO")
  13 - filter("B"."DEPTNO" IS NOT NULL)

统计信息
----------------------------------------------------------
          0  recursive calls
          0  db block gets
         53  consistent gets
          0  physical reads
          0  redo size
        780  bytes sent via SQL*Net to client
        385  bytes received via SQL*Net from client
          2  SQL*Net roundtrips to/from client
          0  sorts (memory)
          0  sorts (disk)
         13  rows processed

可以看到，需要多次访问emp，dept表以及dept表的索引。

修改成：

select a.dname, b.job, sum(b.sal) sum_sal
  from scott.dept a, scott.emp b
 where a.deptno = b.deptno
 group by rollup(a.dname, b.job);

结果如下：

DNAME          JOB          SUM_SAL
-------------- --------- ----------
SALES          CLERK            950
SALES          MANAGER         2850
SALES          SALESMAN        5600
SALES                          9400
RESEARCH       CLERK           1900
RESEARCH       ANALYST         6000
RESEARCH       MANAGER         2975
RESEARCH                      10875
ACCOUNTING     CLERK           1300
ACCOUNTING     MANAGER         2450
ACCOUNTING     PRESIDENT       5000

DNAME          JOB          SUM_SAL
-------------- --------- ----------
ACCOUNTING                     8750
                              29025

执行计划
----------------------------------------------------------
Plan hash value: 503922295

--------------------------------------------------------------------------------
---------
| Id  | Operation                     | Name    | Rows  | Bytes | Cost (%CPU)| T
ime     |
--------------------------------------------------------------------------------
---------
|   0 | SELECT STATEMENT              |         |    14 |   392 |     5  (20)| 0
0:00:01 |
|   1 |  SORT GROUP BY ROLLUP         |         |    14 |   392 |     5  (20)| 0
0:00:01 |
|   2 |   NESTED LOOPS                |         |    14 |   392 |     4   (0)| 0
0:00:01 |
|   3 |    TABLE ACCESS FULL          | EMP     |    14 |   210 |     3   (0)| 0
0:00:01 |
|   4 |    TABLE ACCESS BY INDEX ROWID| DEPT    |     1 |    13 |     1   (0)| 0
0:00:01 |
|*  5 |     INDEX UNIQUE SCAN         | PK_DEPT |     1 |       |     0   (0)| 0
0:00:01 |
--------------------------------------------------------------------------------
---------

Predicate Information (identified by operation id):
---------------------------------------------------

   5 - access("A"."DEPTNO"="B"."DEPTNO")

统计信息
----------------------------------------------------------
          1  recursive calls
          0  db block gets
         23  consistent gets
          0  physical reads
          0  redo size
        750  bytes sent via SQL*Net to client
        385  bytes received via SQL*Net from client
          2  SQL*Net roundtrips to/from client
          1  sorts (memory)
          0  sorts (disk)
         13  rows processed

已选择13行。

 

 

可见，使用rollup只需要访问emp表一次，通过dept表的主键获得rowid表查询相关行，比union all性能要好。