Oracle分頁查詢格式（十）

Oracle的分頁查詢語句基本上可以按照本文給出的格式來進行套用。

Oracle分頁查詢格式（一）：http://yangtingkun.itpub.net/post/468/100278

Oracle分頁查詢格式（二）：http://yangtingkun.itpub.net/post/468/101703

Oracle分頁查詢格式（三）：http://yangtingkun.itpub.net/post/468/104595

Oracle分頁查詢格式（四）：http://yangtingkun.itpub.net/post/468/104867

Oracle分頁查詢格式（五）：http://yangtingkun.itpub.net/post/468/107934

Oracle分頁查詢格式（六）：http://yangtingkun.itpub.net/post/468/108677

Oracle分頁查詢格式（七）：http://yangtingkun.itpub.net/post/468/109834

Oracle分頁查詢格式（八）：http://yangtingkun.itpub.net/post/468/224557

Oracle分頁查詢格式（九）：http://yangtingkun.itpub.net/post/468/224409

Oracle10g的新功能GROUP BY STOPKEY，使得Oracle10g解決了上一篇文章中提到的GROUP BY操作無法分頁的問題。

在10g以前，Oracle的GROUP BY操作必須完全執行完，才能將結果返回給用戶。但是Oracle10g增加了GROUP BY STOPKEY執行路徑，使得用戶在執行GROUP BY操作時，可以根據STOPKEY隨時中止正在運行的操作。

這使得標準分頁函數對于GROUP BY操作重新發揮了作用。

SQL> CREATE TABLE T AS SELECT ROWNUM ID, A.* FROM DBA_OBJECTS A;

表已創建。

SQL> CREATE INDEX IND_T_CREATED ON T (CREATED);

索引已創建。

SQL> ALTER TABLE T MODIFY CREATED NOT NULL;

表已更改。

SQL> ALTER SESSION SET NLS_DATE_FORMAT = 'YYYY-MM-DD HH24:MI:SS';

會話已更改。

SQL> EXEC DBMS_STATS.GATHER_TABLE_STATS(USER, 'T')

PL/SQL 過程已成功完成。

SQL> SET AUTOT ON
SQL> SET TIMING ON
SQL> SELECT *
2 FROM
3 (
4 SELECT ROWNUM RN, A.*
5 FROM
6 (
7 SELECT CREATED, COUNT(*)
8 FROM T
9 GROUP BY CREATED
10 ) A
11 WHERE ROWNUM < 20
12 )
13 WHERE RN >= 10;

RN CREATED COUNT(*)
---------- ------------------- ----------
10 2005-12-19 17:07:57 50
11 2005-12-19 17:07:58 36
12 2005-12-19 17:08:24 10
13 2005-12-19 17:08:25 49
14 2005-12-19 17:08:26 66
15 2005-12-19 17:08:27 62
16 2005-12-19 17:08:28 81
17 2005-12-19 17:08:29 82
18 2005-12-19 17:08:33 1
19 2005-12-19 17:08:35 3

已選擇10行。

已用時間: 00: 00: 00.04

執行計劃
----------------------------------------------------------
Plan hash value: 3639065582

------------------------------------------------------------------------------
| Id | Operation | Name | Rows | Bytes | Cost (%CPU)|
-------------------------------------------------------------------------------
| 0 | SELECT STATEMENT | | 19 | 665 | 1 (0)|
|* 1 | VIEW | | 19 | 665 | 1 (0)|
|* 2 | COUNT STOPKEY | | | | |
| 3 | VIEW | | 973 | 21406 | 1 (0)|
|* 4 | SORT GROUP BY STOPKEY| | 973 | 7784 | 1 (0)|
| 5 | INDEX FULL SCAN | IND_T_CREATED | 984 | 7872 | 1 (0)|
------------------------------------------------------------------------------

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

1 - filter("RN">=10)
2 - filter(ROWNUM<20)
4 - filter(ROWNUM<20)

統計信息
----------------------------------------------------------
1 recursive calls
0 db block gets
67 consistent gets
0 physical reads
0 redo size
730 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)
10 rows processed

SQL> SELECT *
2 FROM
3 (
4 SELECT ROWNUM RN, A.*
5 FROM
6 (
7 SELECT CREATED, COUNT(*)
8 FROM T
9 GROUP BY CREATED
10 ) A
11 )
12 WHERE RN >= 10
13 AND RN < 20;

RN CREATED COUNT(*)
---------- ------------------- ----------
10 2005-12-19 17:09:27 34
11 2005-12-19 17:09:31 29
12 2005-12-19 17:09:40 29
13 2005-12-19 17:09:58 11
14 2005-12-19 17:10:06 6
15 2005-12-19 17:10:12 48
16 2005-12-19 17:10:20 24
17 2005-12-19 17:10:37 8
18 2005-12-19 17:10:40 2
19 2005-12-19 17:10:49 2

已選擇10行。

已用時間: 00: 00: 00.06

執行計劃
----------------------------------------------------------
Plan hash value: 4036621539

------------------------------------------------------------------------------
| Id | Operation | Name | Rows | Bytes | Cost (%CPU)|
-----------------------------------------------------------------------------
| 0 | SELECT STATEMENT | | 973 | 34055 | 14 (36)|
|* 1 | VIEW | | 973 | 34055 | 14 (36)|
| 2 | COUNT | | | | |
| 3 | VIEW | | 973 | 21406 | 14 (36)|
| 4 | HASH GROUP BY | | 973 | 7784 | 14 (36)|
| 5 | INDEX FAST FULL SCAN| IND_T_CREATED | 50359 | 393K| 10 (10)|
------------------------------------------------------------------------------

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

1 - filter("RN">=10 AND "RN"<20)

統計信息
----------------------------------------------------------
1 recursive calls
0 db block gets
73 consistent gets
0 physical reads
0 redo size
724 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)
10 rows processed

通過上面的執行計劃可以看到，無論使用標準分頁函數，還是使用其他方式，Oracle采用的都是10g特有的執行計劃GROUP BY STOPKEY和HASH GROUP BY，與9i的GROUP BY相比較，二者的執行效率都很高，不過利用了標準分頁模式，Oracle可以將STOPKEY推入到查詢最內層，使得Oracle在掃描的開始階段就將結果集限制住。從查詢的邏輯讀和執行時間上也可以看出來，GROUP BY STOPKEY的執行效率更高一些。

從這一點上看，Oracle10g的新功能確實使得查詢效率得到提高。