文章目录

• 连接
• • 七种JOIN介绍
  • 练习
  • • 建表+存储数据
    • 笛卡尔积
    • 内连接
    • 左连接
    • 右连接
    • A表独有
    • B表独有
    • 全连接
    • • 实现方式一：左连接+右连接+公共部分去重
      • 实现方式二：左连接+B独有
    • A独有+B独有
• 文章说明

连接

七种JOIN介绍

练习

建表+存储数据

CREATE TABLE `tbl_emp` (`id` int(11) NOT NULL AUTO_INCREMENT,`name` varchar(20) DEFAULT NULL,`deptId` int(11) DEFAULT NULL,PRIMARY KEY (`id`) ,KEY `fk_dept_id`(`deptId`))ENGINE = InnoDB AUTO_INCREMENT = 1 CHARACTER SET = utf8;CREATE TABLE `tbl_dept` (`id` int(11) NOT NULL AUTO_INCREMENT,`deptName` varchar(30) DEFAULT NULL,`locAdd` varchar(40) DEFAULT NULL,PRIMARY KEY (`id`)) ENGINE = InnoDB AUTO_INCREMENT = 1 CHARACTER SET = utf8;insert into tbl_dept(deptName,locAdd) values('RD',11);insert into tbl_dept(deptName,locAdd) values('HR',12);insert into tbl_dept(deptName,locAdd) values('MK',13);insert into tbl_dept(deptName,locAdd) values('MIS',14);insert into tbl_dept(deptName,locAdd) values('FD',15);insert into tbl_emp(NAME,deptId) values('z3',1);insert into tbl_emp(NAME,deptId) values('z4',1);insert into tbl_emp(NAME,deptId) values('z5',1);insert into tbl_emp(NAME,deptId) values('w5',2);insert into tbl_emp(NAME,deptId) values('w6',2);insert into tbl_emp(NAME,deptId) values('s7',3);insert into tbl_emp(NAME,deptId) values('s8',4);insert into tbl_emp(NAME,deptId) values('s9',51);

笛卡尔积

select * from tbl_emp,tbl_dept;

5条数据和8条数据两两组合，一共40条，结果如下

"id"       "name"     "deptId"    "id"      "deptName"   "locAdd""1"        "z3"        "1"        "5"        "FD"        "15""1"        "z3"        "1"        "4"        "MIS"        "14""1"        "z3"        "1"        "3"        "MK"        "13""1"        "z3"        "1"        "2"        "HR"        "12""1"        "z3"        "1"        "1"        "RD"        "11""2"        "z4"        "1"        "5"        "FD"        "15""2"        "z4"        "1"        "4"        "MIS"        "14""2"        "z4"        "1"        "3"        "MK"        "13""2"        "z4"        "1"        "2"        "HR"        "12""2"        "z4"        "1"        "1"        "RD"        "11""3"        "z5"        "1"        "5"        "FD"        "15""3"        "z5"        "1"        "4"        "MIS"        "14""3"        "z5"        "1"        "3"        "MK"        "13""3"        "z5"        "1"        "2"        "HR"        "12""3"        "z5"        "1"        "1"        "RD"        "11""4"        "w5"        "2"        "5"        "FD"        "15""4"        "w5"        "2"        "4"        "MIS"        "14""4"        "w5"        "2"        "3"        "MK"        "13""4"        "w5"        "2"        "2"        "HR"        "12""4"        "w5"        "2"        "1"        "RD"        "11""5"        "w6"        "2"        "5"        "FD"        "15""5"        "w6"        "2"        "4"        "MIS"        "14""5"        "w6"        "2"        "3"        "MK"        "13""5"        "w6"        "2"        "2"        "HR"        "12""5"        "w6"        "2"        "1"        "RD"        "11""6"        "s7"        "3"        "5"        "FD"        "15""6"        "s7"        "3"        "4"        "MIS"        "14""6"        "s7"        "3"        "3"        "MK"        "13""6"        "s7"        "3"        "2"        "HR"        "12""6"        "s7"        "3"        "1"        "RD"        "11""7"        "s8"        "4"        "5"        "FD"        "15""7"        "s8"        "4"        "4"        "MIS"        "14""7"        "s8"        "4"        "3"        "MK"        "13""7"        "s8"        "4"        "2"        "HR"        "12""7"        "s8"        "4"        "1"        "RD"        "11""8"        "s9"        "51"        "5"        "FD"        "15""8"        "s9"        "51"        "4"        "MIS"        "14""8"        "s9"        "51"        "3"        "MK"        "13""8"        "s9"        "51"        "2"        "HR"        "12""8"        "s9"        "51"        "1"        "RD"        "11"

内连接

SELECT * FROM tbl_emp a INNER JOIN tbl_dept b ON a.deptId = b.id;

左连接

SELECT * FROM tbl_emp a LEFT JOIN tbl_dept b ON a.deptId = b.id;

右连接

SELECT * FROM tbl_emp a RIGHT JOIN tbl_dept b ON a.deptId = b.id;

A表独有

SELECT * FROM tbl_emp a LEFT JOIN tbl_dept b ON a.deptId = b.id WHERE b.id is null;

B表独有

SELECT * FROM tbl_emp a RIGHT JOIN tbl_dept b ON a.deptId = b.id WHERE a.deptId is null;

全连接

尝试换一种方式实现：A的独有+共有+B的独有

实现方式一：左连接+右连接+公共部分去重

SELECT * FROM tbl_emp a LEFT JOIN tbl_dept b ON a.deptId = b.id UNION SELECT * FROM tbl_emp a RIGHT JOIN tbl_dept b ON a.deptId = b.id;

实现方式二：左连接+B独有

SELECT * FROM tbl_emp a LEFT JOIN tbl_dept b ON a.deptId = b.id UNION SELECT * FROM tbl_emp a RIGHT JOIN tbl_dept b ON a.deptId = b.id WHERE a.deptId is null;

A独有+B独有

SELECT * FROM tbl_emp a LEFT JOIN tbl_dept b ON a.deptId = b.id WHERE b.id is null UNION SELECT * FROM tbl_emp a RIGHT JOIN tbl_dept b ON a.deptId = b.id WHERE a.deptId is null;

文章说明

本文章为本人学习尚硅谷的学习笔记，文章中大部分内容来源于尚硅谷视频（点击学习尚硅谷相关课程），也有部分内容来自于自己的思考，发布文章是想帮助其他学习的人更方便地整理自己的笔记或者直接通过文章学习相关知识，如有侵权请联系删除，最后对尚硅谷的优质课程表示感谢。

来源地址：https://blog.csdn.net/laodanqiu/article/details/131233741