优化查询使用NOT EXIST

Question

我想用在下面的查询我怎么可以这样做NOT EXIST优化我的查询，也请您解释一下它的执行计划

Select I_Ftn, I_Col, count(c.i_id_num) cnt 
From DSCL_ALL.W_CALENDER c 
Where c.UNIT_CODE= '01' 
AND c.i_g_vill = '45' 
and c.i_g_code = '1' 
and c.survey_year = '2012-2013' 
and c.i_number not in (select m.m_indent from w_mill_pur m where m.unit_code = c.unit_code and m.m_vill = c.i_g_vill and m.m_grow = c.i_g_code) 
Group By I_Ftn, I_Col 
ORDER BY I_ftn, I_col) 

Answer 1

你可以试试这个：

Select I_Ftn, I_Col, count(c.i_id_num) cnt 
From DSCL_ALL.W_CALENDER c 
Where c.UNIT_CODE= '01' 
AND c.i_g_vill = '45' 
and c.i_g_code = '1' 
and c.survey_year = '2012-2013' 
and not exists (select 1 from w_mill_pur m where m.unit_code = c.unit_code and m.m_vill = c.i_g_vill and m.m_grow = c.i_g_code and m.m_indent = c.i_number) 
Group By I_Ftn, I_Col 
ORDER BY I_ftn, I_col) 

由于添加了where子句，因此效率更高：Oracle能够运行更多筛选子查询，然后仅测试结果集是否为空。 您可能还需要检查你有一个（unit_code，m_vill，m_grow，m.m_indent）为w_mill_pur指数。

的“不”的方式需要在主查询（子查询结果与主一套）一个更加入。

问候，

Answer 2

有 “NOT IN” 和 “NOT EXISTS” 之间的区别。请按照链接通过ASKTOM - optmizing`不IN`条件时

http://asktom.oracle.com/pls/asktom/f?p=100:11:0::NO::P11_QUESTION_ID:442029737684