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  • select min from 连接

    预先准备

    create table p(
           name varchar2(10)
    );
    
    insert into p values('黄伟福');
    insert into p values('赵洪');
    insert into p values('杨华');

    每条语句执行三次插入

    select rowid,p.* from p;

    select distinct * from p;

     查询最小rowID,只返回了一条数据

    select min(rowid) from p p1 where p1.name = p1.name

     查询每个重复名字的最小rowID,注意子查询返回的是3条数据,并不是一条,思考一下具体执行顺序

    select rowid,p1.* from p p1 where rowid = (select min(rowid) from p p2 where p1.name = p2.name);

    删除重复数据,只保存数据中的最小rowID ,然后查询

    delete from p p1 where rowid > (select min(rowid) from p p2 where p1.name = p2.name);
    select rowid,p.* from p;

    再次把数据补齐,然后查询,结果

    select  p1.name,p2.name from p p1,p p2 where p1.name = p2.name

    全部查询,仔细看数据

    select  p1.rowid,p1.name,p2.rowid,p2.name from p p1,p p2 where p1.name = p2.name

     还是9条数据时  

    select  min(p1.rowid) from p p1,p p2 where p1.name = p2.name

    结果

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  • 原文地址:https://www.cnblogs.com/duanwandao/p/9879714.html
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