mysql的表連接（ left | right ）join
阿新 • • 發佈：2017-12-18
num str value creat sele mar arch function clas
測試MYSQL表關於內外連接
表一：雇員表（雇員ID,雇員名稱，雇員入職時間，薪水，部門號）
create table empo(
empoid int(6) not null primary key auto_increment,
empname varchar(32) not null,
empdate datetime not null,
salary int(6) not null ,
deptno int(6) not null
)engine=innodb charset=utf8
insert into empo values(1,‘zhangsan‘,‘2012-2-20 10:00:00‘,6000,1);
insert into empo values(2,‘lisi‘,‘2013-2-20 10:00:00‘,6000,2);
insert into empo values(3,‘王五‘,‘2014-2-20 10:00:00‘,6000,1);
insert into empo values(4,‘趙六 ‘,‘2015-2-20 10:00:00‘,6000,3);
insert into empo values(5,‘趙六 ‘,‘2015-2-20 10:00:00‘,6000,6);
insert into empo values(6,‘趙六 ‘,‘2015-2-20 10:00:00‘,6000,8);
表二（部門號，部門名稱）
create table dept(deptid int(6) primary key ,
deptname varchar(32) not null
)engine=innodb charset=utf8
insert into dept values(1,‘xinzhengbu‘);
insert into dept values(2,‘jixubu‘);
insert into dept values(3,‘yunying‘);
insert into dept values(3,‘shejibu‘);
題目：
例1：內連接（內連接實際上就是利用 where 子句對兩張表形成的笛卡爾積進行篩選,）
mysql> select * from empo,dept;
+--------+----------+---------------------+--------+--------+--------+------------+
| empoid | empname | empdate | salary | deptno | deptid | deptname |
+--------+----------+---------------------+--------+--------+--------+------------+
| 1 | zhangsan | 2012-02-20 10:00:00 | 6000 | 1 | 1 | xinzhengbu |
| 2 | lisi | 2013-02-20 10:00:00 | 6000 | 2 | 1 | xinzhengbu |
| 3 | 王五 | 2014-02-20 10:00:00 | 6000 | 1 | 1 | xinzhengbu |
| 4 | 趙六 | 2015-02-20 10:00:00 | 6000 | 3 | 1 | xinzhengbu |
| 1 | zhangsan | 2012-02-20 10:00:00 | 6000 | 1 | 2 | jixubu |
| 2 | lisi | 2013-02-20 10:00:00 | 6000 | 2 | 2 | jixubu |
| 3 | 王五 | 2014-02-20 10:00:00 | 6000 | 1 | 2 | jixubu |
| 4 | 趙六 | 2015-02-20 10:00:00 | 6000 | 3 | 2 | jixubu |
| 1 | zhangsan | 2012-02-20 10:00:00 | 6000 | 1 | 3 | yunying |
| 2 | lisi | 2013-02-20 10:00:00 | 6000 | 2 | 3 | yunying |
| 3 | 王五 | 2014-02-20 10:00:00 | 6000 | 1 | 3 | yunying |
| 4 | 趙六 | 2015-02-20 10:00:00 | 6000 | 3 | 3 | yunying |
| 1 | zhangsan | 2012-02-20 10:00:00 | 6000 | 1 | 4 | shejibu |
| 2 | lisi | 2013-02-20 10:00:00 | 6000 | 2 | 4 | shejibu |
| 3 | 王五 | 2014-02-20 10:00:00 | 6000 | 1 | 4 | shejibu |
| 4 | 趙六 | 2015-02-20 10:00:00 | 6000 | 3 | 4 | shejibu |
+--------+----------+---------------------+--------+--------+--------+------------+
16 rows in set (0.00 sec)
mysql> select * from empo inner join dept;
+--------+----------+---------------------+--------+--------+--------+------------+
| empoid | empname | empdate | salary | deptno | deptid | deptname |
+--------+----------+---------------------+--------+--------+--------+------------+
| 1 | 張三 | 2012-02-20 10:00:00 | 6000 | 1 | 1 | xinzhengbu |
| 2 | 李四 | 2013-02-20 10:00:00 | 6000 | 2 | 1 | xinzhengbu |
| 3 | 王五 | 2014-02-20 10:00:00 | 6000 | 1 | 1 | xinzhengbu |
| 4 | 趙六 | 2015-02-20 10:00:00 | 6000 | 3 | 1 | xinzhengbu |
| 1 | 張三 | 2012-02-20 10:00:00 | 6000 | 1 | 2 | jixubu |
| 2 | 李四 | 2013-02-20 10:00:00 | 6000 | 2 | 2 | jixubu |
| 3 | 王五 | 2014-02-20 10:00:00 | 6000 | 1 | 2 | jixubu |
| 4 | 趙六 | 2015-02-20 10:00:00 | 6000 | 3 | 2 | jixubu |
| 1 | 張三 | 2012-02-20 10:00:00 | 6000 | 1 | 3 | yunying |
| 2 | 李四 | 2013-02-20 10:00:00 | 6000 | 2 | 3 | yunying |
| 3 | 王五 | 2014-02-20 10:00:00 | 6000 | 1 | 3 | yunying |
| 4 | 趙六 | 2015-02-20 10:00:00 | 6000 | 3 | 3 | yunying |
| 1 | 張三 | 2012-02-20 10:00:00 | 6000 | 1 | 4 | shejibu |
| 2 | 李四 | 2013-02-20 10:00:00 | 6000 | 2 | 4 | shejibu |
| 3 | 王五 | 2014-02-20 10:00:00 | 6000 | 1 | 4 | shejibu |
| 4 | 趙六 | 2015-02-20 10:00:00 | 6000 | 3 | 4 | shejibu |
+--------+----------+---------------------+--------+--------+--------+------------+
16 rows in set (0.00 sec)
上面兩個SQL等價的。
下面是加where條件的等價SQL(select * from empo,dept where deptno=deptid;)
mysql> select * from empo inner join dept on deptno=deptid;
+--------+----------+---------------------+--------+--------+--------+------------+
| empoid | empname | empdate | salary | deptno | deptid | deptname |
+--------+----------+---------------------+--------+--------+--------+------------+
| 1 | 張三 | 2012-02-20 10:00:00 | 6000 | 1 | 1 | xinzhengbu |
| 3 | 王五 | 2014-02-20 10:00:00 | 6000 | 1 | 1 | xinzhengbu |
| 2 | 李四 | 2013-02-20 10:00:00 | 6000 | 2 | 2 | jixubu |
| 4 | 趙六 | 2015-02-20 10:00:00 | 6000 | 3 | 3 | yunying |
+--------+----------+---------------------+--------+--------+--------+------------+
4 rows in set (0.00 sec)
例2：左連接
mysql> select * from empo left join dept on deptno=deptid;
+--------+----------+---------------------+--------+--------+--------+------------+
| empoid | empname | empdate | salary | deptno | deptid | deptname |
+--------+----------+---------------------+--------+--------+--------+------------+
| 1 | 張三 | 2012-02-20 10:00:00 | 6000 | 1 | 1 | xinzhengbu |
| 2 | 李四 | 2013-02-20 10:00:00 | 6000 | 2 | 2 | jixubu |
| 3 | 王五 | 2014-02-20 10:00:00 | 6000 | 1 | 1 | xinzhengbu |
| 4 | 趙六 | 2015-02-20 10:00:00 | 6000 | 3 | 3 | yunying |
+--------+----------+---------------------+--------+--------+--------+------------+
4 rows in set (0.00 sec)
例3：右連接
mysql> select * from empo right join dept on deptno=deptid;
+--------+----------+---------------------+--------+--------+--------+------------+
| empoid | empname | empdate | salary | deptno | deptid | deptname |
+--------+----------+---------------------+--------+--------+--------+------------+
| 1 | 張三 | 2012-02-20 10:00:00 | 6000 | 1 | 1 | xinzhengbu |
| 3 | 王五 | 2014-02-20 10:00:00 | 6000 | 1 | 1 | xinzhengbu |
| 2 | 李四 | 2013-02-20 10:00:00 | 6000 | 2 | 2 | jixubu |
| 4 | 趙六 | 2015-02-20 10:00:00 | 6000 | 3 | 3 | yunying |
| NULL | NULL | NULL | NULL | NULL | 4 | shejibu |
+--------+----------+---------------------+--------+--------+--------+------------+
5 rows in set (0.00 sec)
例4：將子查詢替換成連接
表1
mysql> select * from empo;
+--------+----------+---------------------+--------+--------+
| empoid | empname | empdate | salary | deptno |
+--------+----------+---------------------+--------+--------+
| 1 | 張三 | 2012-02-20 10:00:00 | 6000 | 1 |
| 2 | 李四 | 2013-02-20 10:00:00 | 6000 | 2 |
| 3 | 王五 | 2014-02-20 10:00:00 | 6000 | 1 |
| 4 | 趙六 | 2015-02-20 10:00:00 | 6000 | 3 |
| 5 | 趙六 | 2015-02-20 10:00:00 | 6000 | 6 |
| 6 | 趙六 | 2015-02-20 10:00:00 | 6000 | 8 |
+--------+----------+---------------------+--------+--------+
6 rows in set (0.00 sec)
表2
mysql> select * from dept;
+--------+------------+
| deptid | deptname |
+--------+------------+
| 1 | xinzhengbu |
| 2 | jixubu |
| 3 | yunying |
| 4 | shejibu |
+--------+------------+
4 rows in set (0.00 sec)
題目1、找出雇員不在部門表中的用戶（雇員ID號為5,6的不在部門列表中）
select * from empo where deptno not in (select deptid from dept)
子查詢寫法
mysql> select * from empo where deptno not in (select deptid from dept);
+--------+---------+---------------------+--------+--------+
| empoid | empname | empdate | salary | deptno |
+--------+---------+---------------------+--------+--------+
| 5 | 趙六 | 2015-02-20 10:00:00 | 6000 | 6 |
| 6 | 趙六 | 2015-02-20 10:00:00 | 6000 | 8 |
+--------+---------+---------------------+--------+--------+
內連接寫法(和上面寫法同等）
mysql> select * from empo left join dept on empo.deptno=dept.deptid where deptid is NULL;
+--------+---------+---------------------+--------+--------+--------+----------+
| empoid | empname | empdate | salary | deptno | deptid | deptname |
+--------+---------+---------------------+--------+--------+--------+----------+
| 5 | 趙六 | 2015-02-20 10:00:00 | 6000 | 6 | NULL | NULL |
| 6 | 趙六 | 2015-02-20 10:00:00 | 6000 | 8 | NULL | NULL |
+--------+---------+---------------------+--------+--------+--------+----------+
說明：mysql中join中使用where和on的區別
1.(left|right)join... on.. and 的寫法：是先處理on後面的條件，在處理表之間的連接
2.(left|rgint)join... on.. where的寫法： 是先表left連接，在處理where條件mysql的表連接（ left | right ）join