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  • 数据库的左连接,右连接,内链接:

    先建立数据库,代码如下:

    create database if not exists "emp";

    use emp;

    drop table if exists "dept";

    create table dept( `depid` varchar(50) NOT NULL,    `deptname` varchar(100) default NULL,  PRIMARY KEY  (`depid`) )

    engine=innodb default charset=utf-8;

    insert into dept(`depid`,`deptname`) values ('01','部门1'),('02','部门2'),('03','部门3'),('04','部门4');  

    drop table if exists "emp";

    create table emp (`empid` varchar(50) NOT NULL,   `empname` varchar(50) default NULL,    `depid` varchar(50) default NULL,PRIMARY KEY  (`empid`) ) engine=innodb default charset=utf-8;

    insert into emp(`empid`,`empname`,`depid`) values ('0001','柳梦璃','01'),('0002','韩菱纱','01'),('0003','云天河','02'),('0004','慕容紫英','03'),('0005','玄霄',NULL),('0006','九天玄女',NULL); 

    左连接:select * from dept d left join emp e where d.depid=e.empid;

    右连接:select * from dept d right join emp e where d.depid=e.empid;

    内链接:select * from dept d innner/union join emp e where d.depid=e.empid;

    (内链接可以省略inner/union关键字)

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  • 原文地址:https://www.cnblogs.com/zhouzetian/p/6594096.html
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