Oracle Minus关键字
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]
这两个结果集结构一致才有意义。
--------------------------------------------
//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
感谢 http://blog.csdn.net/greenappple/article/details/7073349