Oracle Minus 取差集

Oracle Minus关键字
  SQL中的MINUS关键字
  SQL中有一个MINUS关键字,它运用在两个SQL语句上,它先找出第一条SQL语句所产生的结果,然后看这些结果有没有在第二个SQL语句的结果中。如果有的话,那这一笔记录就被去除,而不会在最后的结果中出现。如果第二个SQL语句所产生的结果并没有存在于第一个SQL语句所产生的结果内,那这笔资料就被抛弃,其语法如下:
  [SQL Segment 1]
  MINUS
  [SQL Segment 2]
--------------------------------------------
//创建表1
create table test1
(
 name varchar(10),
 sex varchar(10),
);

insert into test1 values('test','female');
insert into test1 values('test1','female');
insert into test1 values('test1','female');
insert into test1 values('test11','female');
insert into test1 values('test111','female');

//创建表2
create table test2
(
 name varchar(10),
 sex varchar(10),
);
insert into test1 values('test','female');
insert into test1 values('test2','female');
insert into test1 values('test2','female');
insert into test1 values('test22','female');
insert into test1 values('test222','female');
-------------------------------------------

select * from test1 minus select * from test2;

结果:

NAME       SEX            
---------- ----------
test1      female            
test11     female 
test111    female
-----------------------------------------------------------

select * from test2 minus select * from test1;

结果:

NAME       SEX            
---------- ----------
test2      female            
test22     female 
test222    female

结论:Minus返回的总是左边表中的数据,它返回的是差集。注意:minus有剃重作用

==========================================================
 下面是我做的实验,很明显能够看出MINUS的效率,made_order共23万笔记录,charge_detail共17万笔记录

性能比较:
  SELECT order_id FROM made_order
  MINUS
  SELECT order_id FROM charge_detail
  1.14 sec
  
  SELECT a.order_id FROM made_order a
  WHERE NOT exists (
   SELECT order_id
   FROM charge_detail
   WHERE order_id = a.order_id
   )
  18.19 sec
  
  SELECT order_id FROM made_order
  WHERE order_id NOT in (
   SELECT order_id
   FROM charge_detail
   )
  20.05 sec
  
  还有其它一下关键字:
  INTERSECT (交集)
  UNION ALL 并集

posted @ 2014-05-29 14:18  jianhong  阅读(146)  评论(0编辑  收藏  举报