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]
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//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‘);
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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
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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