单表查询
MySQL [stu]> select * from student where sage > 18;
MySQL [stu]> select * from student where sage > 18 and sdept = "IS";
多表查询
建立了四个表
MySQL [stu2]> create table class(
-> id int(11) not null auto_increment,
-> name varchar(10) default null,
-> primary key (id)
-> )engine=innodb default charset=utf8mb4
-> ;
MySQL [stu2]> create table teacher(
-> id int(11) not null auto_increment,
-> name varchar(10) default null,
-> age int(3) default null,
-> phone char(11) default null,
-> primary key (id)
-> );
MySQL [stu2]> create table student(
-> id int auto_increment primary key,
-> name varchar(10),
-> age int(3),
-> class_id int,
-> foreign key(class_id) references class(id)
-> );
MySQL [stu2]> create table class2teacher(
-> id int auto_increment primary key,
-> class_id int,
-> teacher_id int,
-> foreign key(class_id) references class(id),
-> foreign key(teacher_id) references teacher(id)
-> );
MySQL [stu2]> insert into class(name) values
-> ("云计算1810"),
-> ("云计算1901"),
-> ("云计算1902");
MySQL [stu2]> insert into teacher(name,age,phone) values
-> ("奇哥", 18, "13733878989"),
-> ("强哥", 28, "15633878989"),
-> ("磊哥", 30, "13933878989"),
-> ("闫老师", 18, "13633878989");
MySQL [stu2]> insert into student(name,age,class_id) values
-> ("黛玉", 18, 3), ("钦文", 19, 3),("马邦德", 30, 1),
-> ("九筒", 48, 1),("六子", 36, 2),("汤师爷", 18, 2),
-> ("麻匪", 18,2),
-> ("黛玉", 18,2);
MySQL [stu2]> insert into class2teacher(class_id,teacher_id) values
-> (1,1),(1,2),(2,1),(2,2),(2,3),(3,1),(3,3);
- 查询每个班级的所有学员的姓名
MySQL [stu2]> select class.name,student.name
-> from class,student
-> where class.id=student.class_id;
- 查询学生马邦德的班级名
MySQL [stu2]> select class.name,student.name
->from student,class
->where student.name="马邦德"
->and student.class_id=class.id;
3.查询磊哥教的学生
MySQL [stu2]> select teacher.name,class.name,student.name
->from teacher,class,class2teacher,student
->where teacher.name="磊哥" and
->teacher.id=class2teacher.teacher_id and
->class2teacher.class_id = class.id and
->class.id=student.class_id;
- 查询黛玉的老师（注意，有两个黛玉）
MySQL [stu2]> select student.id,student.name,teacher.name
->from student,teacher,class2teacher
->where student.name="黛玉" and
->student.class_id=class2teacher.class_id and
->class2teacher.teacher_id=teacher.id ;
- 查询云计算1901班的所有老师
MySQL [stu2]> select teacher.name,class.name
-> from teacher,class,class2teacher
-> where class.name="云计算1901" and
->class.id=class2teacher.class_id and
->class2teacher.teacher_id=teacher.id;
- 查询马邦德班的所有学生
MySQL [stu2]> select A.name
->from student A
->where A.class_id =
->(
->select B.class_id
->from student B
->where B.name="马邦德"
->);
- 查询奇哥教的所有班级（join）
MySQL [stu2]> select teacher.name,class.name from teacher join class join class2teacher on teacher.id = class2teacher.teacher_id and class2teacher.class_id=class.id where teacher.name="奇哥";
