标签：duration 院校 中比 bsp 哪些 click col 表关联 连接查询
? 查询teacher和course表中所有的数据
? select * from teacher,course;
? select name,courseid,course.id,cname from teacher,course where teacher.courseid=course.id;
在关联的两张表中，把满足条件的数据筛选出来
select 字段,... ...
from 表1
inner join 表2
on 条件
inner join 表3
on 条件
-- 使用内连接查询teacher和course 表中的数据（姓名，年龄，课程名称，课时） select t.name,t.age,c.cname,c.cduration from teacher as t inner join course as c on t.course_id=c.id; -- 查询学员的姓名，年龄，所在班级名称，专业名称 并筛选出1902的学员 select s.name,s.age,c.classname,m.m_name from student as s inner join classinfo as c on s.class_id=c.id inner join major as m on s.major_id=m.id where c.classname=‘1902‘; -- 查询学员的姓名，毕业院校，所在班级，考试科目，考试成绩 select s.name,s.school,c.classname,course.cname,sc.score from student as s inner join classinfo as c on s.class_id=c.id inner join score as sc on s.id=sc.stu_id inner join course on sc.course_id = course.id;
1.左外链接
作用：(1)左表中所有的数据都会查询出来（即便不满足条件）
(2)将右表中满足关联条件的数据查询出来
(3)关键不上的数据关联字段将以null作为填充（查询哪些课程没有老师去讲 就用左外链）
语法：select 字
from A left join B
on 关联条件
-- 左外链接，左表：course 右表：teacher -- 关联条件：teacher.course_id=course.id -- 以左表为主 左表的id都显示出来 查询右表关联信息，未关联到的信息显示为null,一般用来查询null的值 select * from course left join teacher on teacher.course_id = course.id where teacher.id is null;
? 2.右外链接
? 作用：1.右表中所有的数据都会查询出来（即便不满足条件）
2.将左表中满足关联条件的数据查询出来
3.关键不上的数据关联字段将以null作为填充
? 语法：select 字段
from A right join B
on 关键条件
-- 右外链接，左表:teacher,右表：course, -- 关联条件：teacher.course_id=course.id select * from teacher right join course on teacher.course_id = course.id where teacher.id is null;
-- 练习：查询没有参加考试的学生 select student.name,score.score from student left join score on student.id=score.stu_id where score.score is null;
1.什么是子查询：将一个查询的结果作为外侧操作的一个条件出现
2.语法：select ... from 表名 where 条件=(select ...);
-- 查询student表中比‘李四’年龄大的学员的信息 select * from student where age>(select age from student where name=‘李四‘);
1 -- 练习：1、查询考过‘王老师’老师所教课程的学校的信息 2 -- 方法1 3 select * from student where id in( 4 select stu_id from score where course_id=( 5 select course_id from teacher where name=‘王老师‘ 6 ) 7 ); 8 -- 方法2 9 select s.name,s.school 10 from student as s 11 inner join score as sc 12 on s.id =sc.stu_id 13 inner join teacher as t 14 on t.course_id=sc.course_id 15 where t.name=‘王老师‘; 16 17 -- 练习：2、查询在score表中有成绩的学员的信息 18 select * from student where id in(select stu_id from score); 19 20 -- 练习：3、查询‘python基础‘课程并且分数在80分以上的学员的姓名和学校 21 -- 方法1 22 select student.name,student.school from 23 student left join score 24 on student.id = score.stu_id 25 left join course 26 on score.course_id = course.id 27 where score>80 and cname=‘python基础‘; 28 -- 方法2 29 select name,school from student where id in( 30 select stu_id from score where score>80 and course_id = ( 31 select id from course where cname=‘python基础‘ 32 ) 33 ); 34 35 -- 练习：4、查询和‘张三’相同班级以及相同专业的同学的信息 36 -- 方法1 37 select student.name,classinfo.classname,major.m_name from 38 student left join classinfo 39 on student.class_id=classinfo.id 40 left join major 41 on student.major_id=major.id 42 where class_id=(select class_id from student where name=‘张三‘) 43 and major_id=(select major_id from student where name=‘张三‘) 44 and student.name!=‘张三‘; 45 -- 方法2 46 select student.name,classinfo.classname,major.m_name 47 from student 48 inner join classinfo 49 on student.class_id=classinfo.id 50 inner join major 51 on student.major_id=major.id 52 where class_id=(select class_id from student where name=‘张三‘) 53 and major_id=(select major_id from student where name=‘张三‘) 54 and student.name!=‘张三‘;
标签：duration 院校 中比 bsp 哪些 click col 表关联 连接查询
原文地址：https://www.cnblogs.com/maplethefox/p/11167131.html
