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循序渐进---hints-Hints for Optimization Approaches and Goals
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下一篇 2008-04-09 15:07:47
/ 个人分类:sql学习
ALL_ROWSFIRST_ROWS(n)CHOOSERULE1. ALL_ROWS
SQL> SELECT /*+ ALL_ROWS */ count(*) from t;
COUNT(*)
----------
500
Elapsed: 00:00:00.09
Execution Plan
----------------------------------------------------------
0 SELECT STATEMENT ptimizer=HINT: ALL_ROWS (Cost=98 Card=1)
1 0 SORT (AGGREGATE)
2 1 TABLE ACCESS (FULL) OF 'T' (Cost=98 Card=500)
2.first rows(n)
SQL> select /*+ first_rows(10) */ * from test1 where rownum<1;
no rows selected
Elapsed: 00:00:00.08
Execution Plan
----------------------------------------------------------
0 SELECT STATEMENT ptimizer=HINT: FIRST_ROWS (Cost=2 Card=1 B
ytes=177)
1 0 COUNT (STOPKEY)
2 1 TABLE ACCESS (FULL) OF 'TEST1' (Cost=2 Card=11 Bytes=194
7)
3.choose
SQL> select /*+ choose */ * from test1 where rownum<1;
no rows selected
Elapsed: 00:00:00.03
Execution Plan
----------------------------------------------------------
0 SELECT STATEMENT ptimizer=HINT: CHOOSE
1 0 COUNT (STOPKEY)
2 1 TABLE ACCESS (FULL) OF 'TEST1'
4.rule
SQL> select /* rule */ * from test1 where rownum<1;
no rows selected
Elapsed: 00:00:00.00
Execution Plan
----------------------------------------------------------
0 SELECT STATEMENT ptimizer=CHOOSE
1 0 COUNT (STOPKEY)
2 1 TABLE ACCESS (FULL) OF 'TEST1'
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