在分页查询时,oracle绑定变量的使用优化
var a number
var b numbervar c numberexec :a:=0exec :b:=10exec :c:=0set serveroutput off;alter session set statistics_level=all;SELECT * FROM (SELECT T1_.*, rownum ROWNUM_ FROM ( SELECT O.* FROM yyf.testa O WHERE 1=1 AND O.CREATE_TIME >= to_date('20150101 12:00:00', 'yyyymmdd hh24:mi:ss') AND O.CREATE_TIME < to_date('20150723 23:59:59', 'yyyymmdd hh24:mi:ss') order by o.CREATE_TIME desc ) T1_ WHERE ROWNUM <= (:a +:b )) WHERE ROWNUM_ >= (:c +1);select * from table(dbms_xplan.display_cursor(null,null,'runstats_last'));
对应的执行计划为:
Plan hash value: 2754511479PLAN_TABLE_OUTPUT-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------| Id | Operation | Name | Starts | E-Rows | A-Rows | A-Time | Buffers | Reads |-----------------------------------------------------------------------------------------------------------| 0 | SELECT STATEMENT | | 1 | | 10 |00:00:20.07 | 684K| 310K||* 1 | VIEW | | 1 | 4133K| 10 |00:00:20.07 | 684K| 310K||* 2 | COUNT STOPKEY | | 1 | | 10 |00:00:20.07 | 684K| 310K|| 3 | VIEW | | 1 | 4133K| 10 |00:00:20.07 | 684K| 310K||* 4 | SORT ORDER BY STOPKEY| | 1 | 4133K| 10 |00:00:20.07 | 684K| 310K||* 5 | TABLE ACCESS FULL | testa | 1 | 4133K| 5351K|00:00:15.40 | 684K| 310K|-----------------------------------------------------------------------------------------------------------PLAN_TABLE_OUTPUT------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------Predicate Information (identified by operation id):--------------------------------------------------- 1 - filter("ROWNUM_">=:C+1) 2 - filter(ROWNUM<=:A+:B) 4 - filter(ROWNUM<=:A+:B) 5 - filter(("O"."CREATE_TIME">=TIMESTAMP' 2015-01-01 12:00:00' AND "O"."CREATE_TIME"
从上面执行计划可以看出,虽然在create_time 是not null ,并且有索引,而且该索引的可选择度非常高。但是该sql依然走的全表扫描。
接着对sql进行如下调整,去掉绑定变量的运算,即把条件由"WHERE ROWNUM <= (:a +:b )) WHERE ROWNUM_ >= (:c +1)" 改为 "WHERE ROWNUM <= (:b )) WHERE ROWNUM_ >= (:c) " ; 其执行计划为:
PLAN_TABLE_OUTPUT---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------| Id | Operation | Name | Starts | E-Rows | A-Rows | A-Time | Buffers | Reads |---------------------------------------------------------------------------------------------------------------------------------| 0 | SELECT STATEMENT | | 1 | | 10 |00:00:00.03 | 49 | 4 ||* 1 | VIEW | | 1 | 10 | 10 |00:00:00.03 | 49 | 4 ||* 2 | COUNT STOPKEY | | 1 | | 10 |00:00:00.03 | 49 | 4 || 3 | VIEW | | 1 | 12 | 10 |00:00:00.03 | 49 | 4 || 4 | TABLE ACCESS BY INDEX ROWID | testa | 1 | 4133K| 10 |00:00:00.03 | 49 | 4 ||* 5 | INDEX RANGE SCAN DESCENDING| IDX_testa_CREATETIME | 1 | 12 | 10 |00:00:00.03 | 36 | 2 |---------------------------------------------------------------------------------------------------------------------------------PLAN_TABLE_OUTPUT------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------Predicate Information (identified by operation id):--------------------------------------------------- 1 - filter("ROWNUM_">=:C) 2 - filter(ROWNUM<=:B) 5 - access("O"."CREATE_TIME"=TIMESTAMP' 2015-01-01 12:00:00')29 rows selected.
posted on 2015-07-27 17:36 阅读( ...) 评论( ...) 收藏