创建一个表:
create table substr_0402(
id number primary key,
count number);插入一些数据;如: insert into substr_0402 values(1,1555);执行下面sql语句:select * from substr_0402 where substr(count,2,3)=555;如何优化这条语句?
一个面试题,请解答!谢谢!
create table substr_0402(
id number primary key,
count number);插入一些数据;如: insert into substr_0402 values(1,1555);执行下面sql语句:select * from substr_0402 where substr(count,2,3)=555;如何优化这条语句?
一个面试题,请解答!谢谢!
CREATE INDEX IDX_FUN ON SUBSTR_0402(substr(TO_CHAR(count),2,3));
查询时用到这个索引:select * from substr_0402 where substr(TO_CHAR(count),2,3)=555;
我试了不行,提示无效的?
我用的是oracle92
alter table substr_0402 modify count varchar2(10);
insert into substr_0402 values(1,1555);
.....SQL> select * from substr_0402; ID COUNT
---------- ----------
1 1555
2 11
3 11
4 11
5 11
6 11
7 11
9 11
29 11
293 11
2932 11 ID COUNT
---------- ----------
29332 11已选择12行。SQL>SQL> select * from substr_0402 where substr(count,2,3)=555; ID COUNT
---------- ----------
1 1555
Execution Plan
----------------------------------------------------------
0 SELECT STATEMENT Optimizer=CHOOSE
1 0 TABLE ACCESS (FULL) OF 'SUBSTR_0402'
Statistics
----------------------------------------------------------
0 recursive calls
0 db block gets
19 consistent gets
0 physical reads
0 redo size
455 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)
1 rows processedSQL> create index i_fun_count on substr_0402(substr(count,2,3));索引已创建。SQL> exec dbms_stats.gather_table_stats(ownname=>'A',tabname=>'SUBSTR_0402',casc
ade=>true);
PL/SQL 过程已成功完成。SQL> select * from substr_0402 where substr(count,2,3)=555; ID COUNT
---------- ----------
1 1555Execution Plan
----------------------------------------------------------
0 SELECT STATEMENT Optimizer=CHOOSE (Cost=2 Card=26 Bytes=208)
1 0 TABLE ACCESS (BY INDEX ROWID) OF 'SUBSTR_0402' (Cost=2 Car
d=26 Bytes=208) 2 1 INDEX (RANGE SCAN) OF 'I_FUN_COUNT' (NON-UNIQUE) (Cost=1
Card=26)Statistics
----------------------------------------------------------
0 recursive calls
0 db block gets
4 consistent gets
0 physical reads
0 redo size
455 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)
1 rows processed