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  • Oracle Minus 取差集

    Oracle Minuskeyword
      SQL中的MINUSkeyword
      SQL中有一个MINUSkeyword,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。假设有的话,那这一笔记录就被去除,而不会在最后的结果中出现。假设第二个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,其语法例如以下:
      [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

    ==========================================================
     以下是我做的实验,非常明显可以看出MINUS的效率,made_order共23万笔记录,charge_detail共17万笔记录

    性能比較:
      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
      
      还有其他一下keyword:
      INTERSECT (交集)
      UNION ALL 并集

     

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  • 原文地址:https://www.cnblogs.com/mfrbuaa/p/4020187.html
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