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