一、普通连表查询
普通的连表查询，把一个select的结果当作另外一个select的参数
SELECT * FROM personnel.person_info where personnel.person_info.part_nid in (SELECT nid from personnel.part WHERE personnel.part.caption="XO股份有限公司公司-技术部-Python开发");
显示结果
+-----+---------+------------------+-------------+----------+----------+---------+ | nid | name | email | phone | part_nid | position | caption | +-----+---------+------------------+-------------+----------+----------+---------+ | 1 | as | as@361way.com | 13800138000 | 5 | Python | NULL | | 2 | ansheng | as@361way.com | 13800138000 | 5 | Python | NULL | | 3 | a | as@361way.com | 13800138000 | 5 | Python | NULL | | 4 | v | as@361way.com | 13800138000 | 5 | Python | NULL | | 5 | b | as@361way.com | 13800138000 | 5 | Python | NULL | | 6 | w | as@361way.com | 13800138000 | 5 | Python | NULL | +-----+---------+------------------+-------------+----------+----------+---------+ 6 rows in set (0.00 sec)
二、join连表查询
join查询如下：
select * from personnel.person_info left join personnel.part on personnel.person_info.part_nid = personnel.part.nid where personnel.part.caption = 'XO股份有限公司公司-技术部-Python开发';
显示结果
+-----+---------+---------------+-------------+----------+----------+---------+------+----------------------------------------------+ | nid | name | email | phone | part_nid | position | caption | nid | caption | +-----+---------+---------------+-------------+----------+----------+---------+------+----------------------------------------------+ | 1 | as | as@361way.com | 13800138000 | 5 | Python | NULL | 5 | XO股份有限公司公司-技术部-Python开发 | | 2 | ansheng | as@361way.com | 13800138000 | 5 | Python | NULL | 5 | XO股份有限公司公司-技术部-Python开发 | | 3 | a | as@361way.com | 13800138000 | 5 | Python | NULL | 5 | XO股份有限公司公司-技术部-Python开发 | | 4 | v | as@361way.com | 13800138000 | 5 | Python | NULL | 5 | XO股份有限公司公司-技术部-Python开发 | | 5 | b | as@361way.com | 13800138000 | 5 | Python | NULL | 5 | XO股份有限公司公司-技术部-Python开发 | | 6 | w | as@361way.com | 13800138000 | 5 | Python | NULL | 5 | XO股份有限公司公司-技术部-Python开发 | +-----+---------+---------------+-------------+----------+----------+---------+------+-----------------------------------------------+ 6 rows in set (0.00 sec)
上面的意思是查询personnel.person_info.part_nid列的字段和personnel.part.nid一样的数据，并且personnel.part.caption = 'XO股份有限公司公司-技术部-Python开发'：
参数
| 实例 | 描述 | |
|---|---|---|
| left join | tb1 left join tb2 | 左外链接 |
| right join | tb1 right join tb2 | 右外链接 |
| inner join | tb1 inner join tb2 | 内链接 |
| Full Join | - | 全外连接 |
| CROSS | - | 交叉链接，又称笛卡尔链接或叉乘 |
left join
- tb1为主，tb2为辅，将A中所有的数据罗列出来
- tb2则只显示与tb1对应的数据
执行以下语句在person_info表中插入一条数据
INSERT INTO personnel.person_info (NAME,email,phone,part_nid,position) VALUES("aa","a@ansheng.me",13800138000,3,"DBA");通过left jion进行查询
mysql> use personnel Database changed mysql> select * from person_info LEFT JOIN part on person_info.part_nid = part.nid WHERE part.nid = 3; +-----+------+--------------+-------------+----------+----------+---------+------+------------------------------------------+ | nid | name | email | phone | part_nid | position | caption | nid | caption | +-----+------+--------------+-------------+----------+----------+---------+------+------------------------------------------+ | 9 | aa | a@ansheng.me | 13800138000 | 3 | DBA | NULL | 3 | XO股份有限公司公司-技术部-DBA | +-----+------+--------------+-------------+----------+----------+---------+------+------------------------------------------+ 1 row in set (0.00 sec)
这样他就只把我们刚刚插入的那条数据查询了除了，即查询person_info表中的内容，part表中的列作为person_info表的查询条件，如果person_info表中的part_nid列如果等于part表中nid列，那么就显示数据。
inner join
- 自动忽略两张表没有建立关联数据
- 只返回两个表中链接字段相等的数据
select * from person_info inner JOIN part on person_info.part_nid = part.nid;
显示结果
+-----+---------+---------------+-------------+----------+----------+---------+-----+---------------------------------------------------+ | nid | name | email | phone | part_nid | position | caption | nid | caption | +-----+---------+---------------+-------------+----------+----------+---------+-----+---------------------------------------------------+ | 1 | as | as@361way.com | 13800138000 | 5 | Python | NULL | 5 | XO股份有限公司公司-技术部-Python开发 | | 2 | ansheng | as@361way.com | 13800138000 | 5 | Python | NULL | 5 | XO股份有限公司公司-技术部-Python开发 | | 3 | a | as@361way.com | 13800138000 | 5 | Python | NULL | 5 | XO股份有限公司公司-技术部-Python开发 | | 4 | v | as@361way.com | 13800138000 | 5 | Python | NULL | 5 | XO股份有限公司公司-技术部-Python开发 | | 5 | b | as@361way.com | 13800138000 | 5 | Python | NULL | 5 | XO股份有限公司公司-技术部-Python开发 | | 6 | w | as@361way.com | 13800138000 | 5 | Python | NULL | 5 | XO股份有限公司公司-技术部-Python开发 | | 9 | aa | a@ansheng.me | 13800138000 | 3 | DBA | NULL | 3 | XO股份有限公司公司-技术部-DBA | +-----+---------+------------ --+-------------+----------+----------+---------+-----+---------------------------------------------------+ 7 rows in set (0.00 sec)
MySQL Full Join的实现
把左右两个表的数据都取出来，不管是否匹配MySQL Full Join的实现 因为MySQL不支持FULL JOIN,下面是替代方法。语法：
select * from A left join B on A.id = B.id (where 条件） union --all可选 select * from A right join B on A.id = B.id （where条件);
三、CROSS连接
如果A和B是两个集合，他们的交叉连接就记为：AxB
mysql> use personnel Database changed mysql> SELECT * from course; +-----+--------+ | Cno | Cname | +-----+--------+ | 1 | 足球 | | 2 | 篮球 | | 3 | 排球 | +-----+--------+ 3 rows in set (0.00 sec) mysql> SELECT * from student; +-----+--------+ | Sno | Name | +-----+--------+ | 1 | 张三 | | 2 | 李四 | | 3 | 王五 | +-----+--------+ 3 rows in set (0.00 sec) mysql> SELECT * FROM course CROSS JOIN student; +-----+--------+-----+--------+ | Cno | Cname | Sno | Name | +-----+--------+-----+--------+ | 1 | 足球 | 1 | 张三 | | 2 | 篮球 | 1 | 张三 | | 3 | 排球 | 1 | 张三 | | 1 | 足球 | 2 | 李四 | | 2 | 篮球 | 2 | 李四 | | 3 | 排球 | 2 | 李四 | | 1 | 足球 | 3 | 王五 | | 2 | 篮球 | 3 | 王五 | | 3 | 排球 | 3 | 王五 | +-----+--------+-----+--------+ 9 rows in set (0.00 sec)
四、一对多，多表查询
创建color表
CREATE TABLE `color` ( `nid` int(11) NOT NULL AUTO_INCREMENT, `title` varchar(32) DEFAULT NULL, PRIMARY KEY (`nid`) ) ENGINE=InnoDB DEFAULT CHARSET=utf8;
往color表中添加两条数据
insert into color(title) values('red'),('yellow');person_info表添加color_nid列，类型是int
alter table person_info add color_nid int;
把person_info表中的color_nid列和color表中的nid列做一个外键关联
alter table person_info add constraint person_ibfk_2 foreign key person_info(`color_nid`) REFERENCES color(`nid`);
往person_info表中插入一条数据：
INSERT INTO personnel.person_info (NAME,email,phone,part_nid,position,color_nid) VALUES("b", "b.ansheng.me",13800138000,3,"DBA",1)查询职位是XO股份有限公司公司-技术部-DBA，颜色是yellow的的人员
SELECT * FROM person_info LEFT JOIN part ON person_info.part_nid = part.nid LEFT JOIN color ON person_info.color_nid = color.nid WHERE color.title = "yellow";
五、多对多关系及查询
先创建三张表
#student(学生表) CREATE TABLE `student` ( `Sno` int(11) NOT NULL AUTO_INCREMENT, `Name` char(20) NOT NULL, PRIMARY KEY (`Sno`) ) ENGINE=InnoDB DEFAULT CHARSET=utf8; #course(课程表) CREATE TABLE `course` ( `Cno` int(11) NOT NULL AUTO_INCREMENT, `Cname` char(10) NOT NULL, PRIMARY KEY (`Cno`) ) ENGINE=InnoDB DEFAULT CHARSET=utf8; #student_course(关系表) CREATE TABLE `student_course` ( `ID` int(11) NOT NULL AUTO_INCREMENT, `Sno` int(11) NOT NULL, `Cno` int(11) NOT NULL, PRIMARY KEY (`ID`) ) ENGINE=InnoDB DEFAULT CHARSET=utf8;
设置外键关联
ALTER TABLE student_course ADD CONSTRAINT student_course_to_student_ibfk_2 FOREIGN KEY student_course (`Sno`) REFERENCES student (`Sno`); ALTER TABLE student_course ADD CONSTRAINT student_course_to_course_ibfk_1 FOREIGN KEY student_course (`Cno`) REFERENCES course (`Cno`);
往三个表中分别插入数据：
#往course(课程表)中插入数据
INSERT INTO course(Cname) VALUES("足球"),("篮球"),("排球");
#往student(学生表)中插入数据
INSERT INTO student(Name) VALUES("张三"),("李四"),("王五");
#student_course(关系表)插入数据
INSERT INTO student_course(Sno,Cno) VALUES(2,1),(2,3),(3,3),(3,1),(1,2),(3,2);显示学生所选的课程SQL指令
SELECT s.Name,C.Cname FROM student_course AS sc LEFT JOIN student AS s ON s.Sno=sc.Sno LEFT JOIN course AS c ON c.Cno=sc.Cno;
结果如下:
+--------+--------+ | Name | Cname | +--------+--------+ | 张三 | 篮球 | | 李四 | 足球 | | 李四 | 排球 | | 王五 | 排球 | | 王五 | 足球 | | 王五 | 篮球 | +--------+--------+ 6 rows in set (0.00 sec)
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