Oracle分页查询语句(二)

及时首著作用多少个例子来注脚分页查询的效能。首先构造一个较大的表作为测试表:

SQL> CREATE TABLE T AS SELECT * FROM
DBA_OBJECTS, DBA_SEQUENCES;

申就创设。

SQL> SELECT COUNT(*) FROM T;

COUNT(*)

457992

首先比少栽分页方法的界别:

SQL> SET AUTOT ON
SQL> COL OBJECT_NAME FORMAT A30
SQL> EXEC DBMS_STATS.GATHER_TABLE_STATS(USER, ‘T’)

PL/SQL 过程都成功做到。

SQL> SELECT OBJECT_ID,
OBJECT_NAME
2 FROM
3 (
4 SELECT ROWNUM RN, OBJECT_ID, OBJECT_NAME
5 FROM
6 (
7 SELECT OBJECT_ID, OBJECT_NAME FROM T
8 )
9 )
10 WHERE RN BETWEEN 11 AND 20;

OBJECT_ID OBJECT_NAME


5807 ALL_APPLY_PROGRESS
1769 ALL_ARGUMENTS
2085 ALL_ASSOCIATIONS
4997 ALL_AUDIT_POLICIES
4005 ALL_BASE_TABLE_MVIEWS
5753 ALL_CAPTURE
5757 ALL_CAPTURE_PARAMETERS
5761 ALL_CAPTURE_PREPARED_DATABASE
5765 ALL_CAPTURE_PREPARED_SCHEMAS
5769 ALL_CAPTURE_PREPARED_TABLES

已选择10行。

Execution Plan

0 SELECT STATEMENT Optimizer=CHOOSE (Cost=864 Card=457992
Bytes=42135264)
1 0 VIEW (Cost=864 Card=457992 Bytes=42135264)
2 1 COUNT
3 2 TABLE ACCESS (FULL) OF ‘T’ (Cost=864 Card=457992
Bytes=9617832)

 

Statistics

0 recursive calls
0 db block gets
8979 consistent gets
7422 physical reads
0 redo size
758 bytes sent via SQL*Net to client
503 bytes received via SQL*Net from client
2 SQL*Net roundtrips to/from client
0 sorts (memory)
0 sorts (disk)
10 rows processed

SQL> SELECT OBJECT_ID,
OBJECT_NAME
2 FROM
3 (
4 SELECT ROWNUM RN, OBJECT_ID, OBJECT_NAME
5 FROM
6 (
7 SELECT OBJECT_ID, OBJECT_NAME FROM T
8 )
9 WHERE ROWNUM <= 20
10 )
11 WHERE RN >= 11;

OBJECT_ID OBJECT_NAME


5807 ALL_APPLY_PROGRESS
1769 ALL_ARGUMENTS
2085 ALL_ASSOCIATIONS
4997 ALL_AUDIT_POLICIES
4005 ALL_BASE_TABLE_MVIEWS
5753 ALL_CAPTURE
5757 ALL_CAPTURE_PARAMETERS
5761 ALL_CAPTURE_PREPARED_DATABASE
5765 ALL_CAPTURE_PREPARED_SCHEMAS
5769 ALL_CAPTURE_PREPARED_TABLES

已选择10行。

Execution Plan

0 SELECT STATEMENT Optimizer=CHOOSE (Cost=864 Card=20 Bytes=1840)
1 0 VIEW (Cost=864 Card=20 Bytes=1840)
2 1 COUNT (STOPKEY)
3 2 TABLE ACCESS (FULL) OF ‘T’ (Cost=864 Card=457992
Bytes=9617832)

 

Statistics

0 recursive calls
0 db block gets
5 consistent gets
0 physical reads
0 redo size
758 bytes sent via SQL*Net to client
503 bytes received via SQL*Net from client
2 SQL*Net roundtrips to/from client
0 sorts (memory)
0 sorts (disk)
10 rows processed

双方执行效用相差大酷,一个索要8000大多逻辑读,而另外一个止需要5只逻辑读。观看二者的施行计划好窥见,多少个执行计划唯一的区别就是次独查询在COUNT这步用了STOPKEY,也就是说,Oracle将ROWNUM
<=
20推入到查询内层,当可查询的尺码的笔录上STOPKEY的值,则Oracle停止查询。

故此,可以预见,拔取第三种方法,在翻页的先河有些查询速度连忙,越到后,功效进一步小,当翻译至最终一页,效率应与率先种形式接近。

SQL> SELECT OBJECT_ID,
OBJECT_NAME
2 FROM
3 (
4 SELECT ROWNUM RN, OBJECT_ID, OBJECT_NAME
5 FROM
6 (
7 SELECT OBJECT_ID, OBJECT_NAME FROM T
8 )
9 WHERE ROWNUM <= 457990
10 )
11 WHERE RN >= 457980;

OBJECT_ID OBJECT_NAME


7128 XCF_I_HANDLE_STATUS
7126 XCF_P
7127 XCF_U1
7142 XDF
7145 XDF_I_DF_KEY
7146 XDF_I_HANDLE_STATUS
7143 XDF_P
7144 XDF_U1
TEST.YANGTINGKUN
TEST4.YANGTINGKUN
YANGTK.YANGTINGKUN

已选择11行。

Execution Plan

0 SELECT STATEMENT Optimizer=CHOOSE (Cost=864 Card=457990
Bytes=42135080)
1 0 VIEW (Cost=864 Card=457990 Bytes=42135080)
2 1 COUNT (STOPKEY)
3 2 TABLE ACCESS (FULL) OF ‘T’ (Cost=864 Card=457992
Bytes=9617832)

 

Statistics

0 recursive calls
0 db block gets
8979 consistent gets
7423 physical reads
0 redo size
680 bytes sent via SQL*Net to client
503 bytes received via SQL*Net from client
2 SQL*Net roundtrips to/from client
0 sorts (memory)
0 sorts (disk)
11 rows processed

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