select sum(sl0000) from xstfxps2 where dhao00 in ( select dhao00 from xstfxps1 where trunc(ywrq00)=trunc(sysdate) and khdm00='500000003913'); 已用时间: 00: 02: 49.04
Execution Plan ---------------------------------------------------------- 0 SELECT STATEMENT Optimizer=CHOOSE 1 0 SORT (AGGREGATE) 2 1 NESTED LOOPS 3 2 TABLE ACCESS (FULL) OF 'XSTFXPS2' 4 2 TABLE ACCESS (BY INDEX ROWID) OF 'XSTFXPS1' 5 4 INDEX (UNIQUE SCAN) OF 'XSTFXPS1_PK' (UNIQUE)
Statistics ---------------------------------------------------------- 0 recursive calls 0 db block gets 17355138 consistent gets 34141 physical reads 2912 redo size 198 bytes sent via SQL*Net to client 275 bytes received via SQL*Net from client 2 SQL*Net roundtrips to/from client 0 sorts (memory) 0 sorts (disk) 1 rows processed 我们看到统计信息里面进行了17355138次逻辑读，34141次物理IO，这是相当吓人的数字。在执行计划里面我们看到表XSTFXPS2来了一次全表扫描。 我们首先看一下这两张表总的数据量： SQL> select count(*) from xstfxps2;
COUNT(*) ---------- 5585018 我们这里看到XSTFXPS2这张表有5585018条记录。 SQL> select count(*) from xstfxps1;
COUNT(*) ---------- 702121 两张表的表结构如下所示： SQL> desc xstfxps1 Name Type Nullable Default Comments ------ ------------ -------- ------- -------- DHAO00 NUMBER(8) LHDH00 NUMBER(8) Y FLDH00 NUMBER(8) Y FPLB00 VARCHAR2(2) Y YWRQ00 DATE Y YWRY00 VARCHAR2(8) Y SHRQ00 DATE Y XSQRRQ DATE Y XSQRRY VARCHAR2(8) Y KHDM00 VARCHAR2(12) XKZH00 VARCHAR2(12) CKDM00 VARCHAR2(2) Y THCKDM VARCHAR2(2) Y XSFSDM VARCHAR2(2) Y FXRYDM VARCHAR2(4) Y SHRYDM VARCHAR2(4) Y SHBJ00 VARCHAR2(1) 'N' FXBJ00 VARCHAR2(1) 'N' SKBJ00 VARCHAR2(2) Y FKDM00 VARCHAR2(2) Y
SQL> desc xstfxps2 Name Type Nullable Default Comments ------ ------------ -------- ------- -------- DHAO00 NUMBER(8) SPDM00 VARCHAR2(8) DJIA00 NUMBER(7,2) 0 FXSL00 NUMBER Y 0 SL0000 NUMBER Y 0 THSL00 NUMBER Y 0 JE0000 NUMBER Y 0 SE0000 NUMBER Y FPBBH0 VARCHAR2(11) Y FPHAO0 VARCHAR2(10) Y RBDH00 NUMBER(8) Y
select index_name,column_name from dba_ind_columns where table_name like 'XSTFXPS%' INDEX_NAME COLUMN_NAME ------------------------------ ----------------------------------- XSTFXPS1_PK DHAO00 XSTFXPS2_PK DHAO00 XSTFXPS2_PK SPDM00
我们看到这两张表除了主键约束外都没有建另外的索引。根据语句的查询情况，我们建立了如下的复合索引： create index idx_xstfxps1_khdm00_ywrq00 on xstfxps1(khdm00,ywrq00) tablespace indx;
为了使用索引，我们必须对原来的日期字段的条件进行一些调整。因为有个trunc()函数的存在，语句将不会使用到索引。我们只要明白trunc(ywrq00)=trunc(sysdate)事实上等同于ywrq00大于trunc(sysdate)，小于trunc(sysdate+1)减去一秒，我们就有了比较好的办法来处理 这个条件。最终改写后的语句如下： select sum(sl0000) from xstfxps2 a, xstfxps1 b where a.dhao00=b.dhao00 and b.khdm00='500000003913' and b.ywrq00 between trunc(sysdate) and trunc(sysdate)+1-1/(24*60*60); Execution Plan ---------------------------------------------------------- 0 SELECT STATEMENT Optimizer=CHOOSE 1 0 SORT (AGGREGATE) 2 1 TABLE ACCESS (BY INDEX ROWID) OF 'XSTFXPS2' 3 2 NESTED LOOPS 4 3 TABLE ACCESS (BY INDEX ROWID) OF 'XSTFXPS1' 5 4 INDEX (RANGE SCAN) OF 'IDX_XSTFXPS1_KHDM00_YWRQ00' (NON-UNIQUE)
6 3 INDEX (RANGE SCAN) OF 'XSTFXPS2_PK' (UNIQUE) Statistics ---------------------------------------------------------- 0 recursive calls 0 db block gets 3 consistent gets 0 physical reads 0 redo size 210 bytes sent via SQL*Net to client 275 bytes received via SQL*Net from client 2 SQL*Net roundtrips to/from client 0 sorts (memory) 0 sorts (disk) 1 rows processed 我们这时候看逻辑IO已经降为3次，语句的执行计划也符合我们的调整目标，创建的索引产生了比较大的效果。这条语句的调整至此告一段落。
