类似groupby的分组计数功能

之前同事发过一个语句，实现的功能比较简单，类似group by的分组计数功能，因为where条件有like，又无法用group by来实现。SELECT a.N0,b.N1,c.N2,d.N3,e.N4,f.N5,g.N6,h.N7,i.N8,j.N9 from (select count(*) N0 from tbl_loginfo_20141110 where keyrecord

之前同事发过一个语句，实现的功能比较简单，类似group by的分组计数功能，因为where条件有like，又无法用group by来实现。
SELECT a.N0,b.N1,c.N2,d.N3,e.N4,f.N5,g.N6,h.N7,i.N8,j.N9 from 
 (select count(*) N0 from tbl_loginfo_20141110 where keyrecord like &＃39;0%&＃39; or keyrecord like &＃39;GJ_0%&＃39;) a,
 (select count(*) N1 from tbl_loginfo_20141110 where keyrecord like &＃39;1%&＃39; or keyrecord like &＃39;GJ_1%&＃39;) b,
 (select count(*) N2 from tbl_loginfo_20141110 where keyrecord like &＃39;2%&＃39; or keyrecord like &＃39;GJ_2%&＃39;) c,
 (select count(*) N3 from tbl_loginfo_20141110 where keyrecord like &＃39;3%&＃39; or keyrecord like &＃39;GJ_3%&＃39;) d,
 (select count(*) N4 from tbl_loginfo_20141110 where keyrecord like &＃39;4%&＃39; or keyrecord like &＃39;GJ_4%&＃39;) e,
 (select count(*) N5 from tbl_loginfo_20141110 where keyrecord like &＃39;5%&＃39; or keyrecord like &＃39;GJ_5%&＃39;) f,
 (select count(*) N6 from tbl_loginfo_20141110 where keyrecord like &＃39;6%&＃39; or keyrecord like &＃39;GJ_6%&＃39;) g,
 (select count(*) N7 from tbl_loginfo_20141110 where keyrecord like &＃39;7%&＃39; or keyrecord like &＃39;GJ_7%&＃39;) h,
 (select count(*) N8 from tbl_loginfo_20141110 where keyrecord like &＃39;8%&＃39; or keyrecord like &＃39;GJ_8%&＃39;) i,
 (select count(*) N9 from tbl_loginfo_20141110 where keyrecord like &＃39;9%&＃39; or keyrecord like &＃39;GJ_9%&＃39;) j;
 
为了了解语句的性能，我做了如下类似的测试： 
select * from v$version;   --Oracle Database 11g Enterprise Edition Release 11.2.0.1.0 - Production
drop table a;
create table a as select * from dba_objects where rownum<=50000;
begin
  for x in 1..6 loop
    insert into a select * from a;
  end loop;
  commit;
end;

select count(*) from a;   --3200000
select bytes/1024/1024 from user_segments where segment_name=&＃39;A&＃39;;  --357M

alter system flush shared_pool;
alter system flush buffer_cache;

SELECT a.N0,b.N1,c.N2,d.N3,e.N4,f.N5,g.N6,h.N7,i.N8,j.N9 from 
 (select count(*) N0 from a where object_name like &＃39;A%&＃39; or object_name like &＃39;V%&＃39;) a,
 (select count(*) N1 from a where object_name like &＃39;B%&＃39; or object_name like &＃39;V%&＃39;) b,
 (select count(*) N2 from a where object_name like &＃39;C%&＃39; or object_name like &＃39;V%&＃39;) c,
 (select count(*) N3 from a where object_name like &＃39;D%&＃39; or object_name like &＃39;V%&＃39;) d,
 (select count(*) N4 from a where object_name like &＃39;E%&＃39; or object_name like &＃39;V%&＃39;) e,
 (select count(*) N5 from a where object_name like &＃39;F%&＃39; or object_name like &＃39;V%&＃39;) f,
 (select count(*) N6 from a where object_name like &＃39;G%&＃39; or object_name like &＃39;V%&＃39;) g,
 (select count(*) N7 from a where object_name like &＃39;H%&＃39; or object_name like &＃39;V%&＃39;) h,
 (select count(*) N8 from a where object_name like &＃39;I%&＃39; or object_name like &＃39;V%&＃39;) i,
 (select count(*) N9 from a where object_name like &＃39;J%&＃39; or object_name like &＃39;V%&＃39;) j;
--58s
alter system flush shared_pool;
alter system flush buffer_cache;

--改写后
select 
sum(case when object_name like &＃39;A%&＃39; or object_name like &＃39;V%&＃39; then 1 else 0 end) N0,
sum(case when object_name like &＃39;B%&＃39; or object_name like &＃39;V%&＃39; then 1 else 0 end) N1, 
sum(case when object_name like &＃39;C%&＃39; or object_name like &＃39;V%&＃39; then 1 else 0 end) N2, 
sum(case when object_name like &＃39;D%&＃39; or object_name like &＃39;V%&＃39; then 1 else 0 end) N3, 
sum(case when object_name like &＃39;E%&＃39; or object_name like &＃39;V%&＃39; then 1 else 0 end) N4, 
sum(case when object_name like &＃39;F%&＃39; or object_name like &＃39;V%&＃39; then 1 else 0 end) N5, 
sum(case when object_name like &＃39;G%&＃39; or object_name like &＃39;V%&＃39; then 1 else 0 end) N6, 
sum(case when object_name like &＃39;H%&＃39; or object_name like &＃39;V%&＃39; then 1 else 0 end) N7, 
sum(case when object_name like &＃39;I%&＃39; or object_name like &＃39;V%&＃39; then 1 else 0 end) N8, 
sum(case when object_name like &＃39;J%&＃39; or object_name like &＃39;V%&＃39; then 1 else 0 end) N9
from a; 

--19s





--对比执行计划：
--前者执行计划：
SQL> explain plan for
  2  SELECT a.N0,b.N1,c.N2,d.N3,e.N4,f.N5,g.N6,h.N7,i.N8,j.N9 from
  3   (select count(*) N0 from a where object_name like &＃39;A%&＃39; or object_name like &＃39;V%&＃39;) a,
  4   (select count(*) N1 from a where object_name like &＃39;B%&＃39; or object_name like &＃39;V%&＃39;) b,
  5   (select count(*) N2 from a where object_name like &＃39;C%&＃39; or object_name like &＃39;V%&＃39;) c,
  6   (select count(*) N3 from a where object_name like &＃39;D%&＃39; or object_name like &＃39;V%&＃39;) d,
  7   (select count(*) N4 from a where object_name like &＃39;E%&＃39; or object_name like &＃39;V%&＃39;) e,
  8   (select count(*) N5 from a where object_name like &＃39;F%&＃39; or object_name like &＃39;V%&＃39;) f,
  9   (select count(*) N6 from a where object_name like &＃39;G%&＃39; or object_name like &＃39;V%&＃39;) g,
 10   (select count(*) N7 from a where object_name like &＃39;H%&＃39; or object_name like &＃39;V%&＃39;) h,
 11   (select count(*) N8 from a where object_name like &＃39;I%&＃39; or object_name like &＃39;V%&＃39;) i,
 12   (select count(*) N9 from a where object_name like &＃39;J%&＃39; or object_name like &＃39;V%&＃39;) j;

Explained.

Elapsed: 00:00:00.15
SQL> @getplan
&＃39;general,outline,starts&＃39;

Enter value for plan type:

PLAN_TABLE_OUTPUT
-----------------------------------------------------------------------------------------
Plan hash value: 2527411742

-------------------------------------------------------------------------------------
| Id  | Operation                    | Name | Rows  | Bytes | Cost (%CPU)| Time     |
-------------------------------------------------------------------------------------
|   0 | SELECT STATEMENT             |      |     1 |   130 |   123K  (1)| 00:24:46 |
|   1 |  NESTED LOOPS                |      |     1 |   130 |   123K  (1)| 00:24:46 |
|   2 |   NESTED LOOPS               |      |     1 |   117 |   111K  (1)| 00:22:17 |
|   3 |    NESTED LOOPS              |      |     1 |   104 | 99032   (1)| 00:19:49 |
|   4 |     NESTED LOOPS             |      |     1 |    91 | 86653   (1)| 00:17:20 |
|   5 |      NESTED LOOPS            |      |     1 |    78 | 74274   (1)| 00:14:52 |
|   6 |       NESTED LOOPS           |      |     1 |    65 | 61895   (1)| 00:12:23 |
|   7 |        NESTED LOOPS          |      |     1 |    52 | 49516   (1)| 00:09:55 |
|   8 |         NESTED LOOPS         |      |     1 |    39 | 37137   (1)| 00:07:26 |
|   9 |          NESTED LOOPS        |      |     1 |    26 | 24758   (1)| 00:04:58 |
|  10 |           VIEW               |      |     1 |    13 | 12379   (1)| 00:02:29 |
|  11 |            SORT AGGREGATE    |      |     1 |    66 |            |          |
|* 12 |             TABLE ACCESS FULL| A    | 91587 |  5903K| 12379   (1)| 00:02:29 |
|  13 |           VIEW               |      |     1 |    13 | 12379   (1)| 00:02:29 |
|  14 |            SORT AGGREGATE    |      |     1 |    66 |            |          |
|* 15 |             TABLE ACCESS FULL| A    |   137K|  8831K| 12379   (1)| 00:02:29 |
|  16 |          VIEW                |      |     1 |    13 | 12379   (1)| 00:02:29 |
|  17 |           SORT AGGREGATE     |      |     1 |    66 |            |          |
|* 18 |            TABLE ACCESS FULL | A    | 85818 |  5531K| 12379   (1)| 00:02:29 |
|  19 |         VIEW                 |      |     1 |    13 | 12379   (1)| 00:02:29 |
|  20 |          SORT AGGREGATE      |      |     1 |    66 |            |          |
|* 21 |           TABLE ACCESS FULL  | A    |   111K|  7158K| 12379   (1)| 00:02:29 |
|  22 |        VIEW                  |      |     1 |    13 | 12379   (1)| 00:02:29 |
|  23 |         SORT AGGREGATE       |      |     1 |    66 |            |          |
|* 24 |          TABLE ACCESS FULL   | A    | 86539 |  5577K| 12379   (1)| 00:02:29 |
|  25 |       VIEW                   |      |     1 |    13 | 12379   (1)| 00:02:29 |
|  26 |        SORT AGGREGATE        |      |     1 |    66 |            |          |
|* 27 |         TABLE ACCESS FULL    | A    | 91587 |  5903K| 12379   (1)| 00:02:29 |
|  28 |      VIEW                    |      |     1 |    13 | 12379   (1)| 00:02:29 |
|  29 |       SORT AGGREGATE         |      |     1 |    66 |            |          |
|* 30 |        TABLE ACCESS FULL     | A    |   228K|    14M| 12379   (1)| 00:02:29 |
|  31 |     VIEW                     |      |     1 |    13 | 12379   (1)| 00:02:29 |
|  32 |      SORT AGGREGATE          |      |     1 |    66 |            |          |
|* 33 |       TABLE ACCESS FULL      | A    | 87981 |  5670K| 12379   (1)| 00:02:29 |
|  34 |    VIEW                      |      |     1 |    13 | 12379   (1)| 00:02:29 |
|  35 |     SORT AGGREGATE           |      |     1 |    66 |            |          |
|* 36 |      TABLE ACCESS FULL       | A    | 84376 |  5438K| 12379   (1)| 00:02:29 |
|  37 |   VIEW                       |      |     1 |    13 | 12379   (1)| 00:02:29 |
|  38 |    SORT AGGREGATE            |      |     1 |    66 |            |          |
|* 39 |     TABLE ACCESS FULL        | A    |   112K|  7251K| 12379   (1)| 00:02:29 |
-------------------------------------------------------------------------------------

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

  12 - filter("OBJECT_NAME" LIKE &＃39;J%&＃39; OR "OBJECT_NAME" LIKE &＃39;V%&＃39;)
  15 - filter("OBJECT_NAME" LIKE &＃39;I%&＃39; OR "OBJECT_NAME" LIKE &＃39;V%&＃39;)
  18 - filter("OBJECT_NAME" LIKE &＃39;H%&＃39; OR "OBJECT_NAME" LIKE &＃39;V%&＃39;)
  21 - filter("OBJECT_NAME" LIKE &＃39;G%&＃39; OR "OBJECT_NAME" LIKE &＃39;V%&＃39;)
  24 - filter("OBJECT_NAME" LIKE &＃39;F%&＃39; OR "OBJECT_NAME" LIKE &＃39;V%&＃39;)
  27 - filter("OBJECT_NAME" LIKE &＃39;E%&＃39; OR "OBJECT_NAME" LIKE &＃39;V%&＃39;)
  30 - filter("OBJECT_NAME" LIKE &＃39;D%&＃39; OR "OBJECT_NAME" LIKE &＃39;V%&＃39;)
  33 - filter("OBJECT_NAME" LIKE &＃39;C%&＃39; OR "OBJECT_NAME" LIKE &＃39;V%&＃39;)
  36 - filter("OBJECT_NAME" LIKE &＃39;B%&＃39; OR "OBJECT_NAME" LIKE &＃39;V%&＃39;)
  39 - filter("OBJECT_NAME" LIKE &＃39;A%&＃39; OR "OBJECT_NAME" LIKE &＃39;V%&＃39;)
  
  
  
  
  
--后者执行计划：  
SQL> explain plan for
  2  select
  3  sum(case when object_name like &＃39;A%&＃39; or object_name like &＃39;V%&＃39; then 1 else 0 end) N0,
  4  sum(case when object_name like &＃39;B%&＃39; or object_name like &＃39;V%&＃39; then 1 else 0 end) N1,
  5  sum(case when object_name like &＃39;C%&＃39; or object_name like &＃39;V%&＃39; then 1 else 0 end) N2,
  6  sum(case when object_name like &＃39;D%&＃39; or object_name like &＃39;V%&＃39; then 1 else 0 end) N3,
  7  sum(case when object_name like &＃39;E%&＃39; or object_name like &＃39;V%&＃39; then 1 else 0 end) N4,
  8  sum(case when object_name like &＃39;F%&＃39; or object_name like &＃39;V%&＃39; then 1 else 0 end) N5,
  9  sum(case when object_name like &＃39;G%&＃39; or object_name like &＃39;V%&＃39; then 1 else 0 end) N6,
 10  sum(case when object_name like &＃39;H%&＃39; or object_name like &＃39;V%&＃39; then 1 else 0 end) N7,
 11  sum(case when object_name like &＃39;I%&＃39; or object_name like &＃39;V%&＃39; then 1 else 0 end) N8,
 12  sum(case when object_name like &＃39;J%&＃39; or object_name like &＃39;V%&＃39; then 1 else 0 end) N9
 13  from a;

Explained.

Elapsed: 00:00:00.01
SQL> @getplan
&＃39;general,outline,starts&＃39;

Enter value for plan type:

PLAN_TABLE_OUTPUT
--------------------------------------------------------------------------------------------
Plan hash value: 3918351354

---------------------------------------------------------------------------
| Id  | Operation          | Name | Rows  | Bytes | Cost (%CPU)| Time     |
---------------------------------------------------------------------------
|   0 | SELECT STATEMENT   |      |     1 |    66 | 12349   (1)| 00:02:29 |
|   1 |  SORT AGGREGATE    |      |     1 |    66 |            |          |
|   2 |   TABLE ACCESS FULL| A    |  3097K|   194M| 12349   (1)| 00:02:29 |
---------------------------------------------------------------------------

Note
-----
   - dynamic sampling used for this statement (level=2)  


可以看出，前者10次全表扫描，后者1次全表扫描。从而时间上也大大降低了。由58s降低到19s。
优化这个sql主要还是思路的转换，难点在于怎样把10次全表扫描转化成1次全表扫描。
在OLAP中，可以加并行使sql速度更快。