学生表mysql查询语句

用mysql创建一个school数据库，建四张学生表tb_student, 记录表tb_record,课程表tb_course表。

下面是简单的mysql基础语句查询

use school;

– 查询所有学生的所有信息
select * from tb_student;

– 查询学生的学号、姓名和家庭住址(投影)
select stu_id, stu_name, stu_addr from tb_student;

– 查询所有课程的名称及学分(投影和别名) —> alias
select cou_name as 课程名称, cou_credit as 学分 from tb_course;

– 查询所有女学生的姓名和出生日期(筛选)
select stu_name, stu_birth from tb_student where stu_sex=0;

– 查询所有80后学生的姓名、性别和出生日期(筛选)
select stu_name, stu_sex, stu_birth
from tb_student
where stu_birth>=‘1980-1-1’ and stu_birth<=‘1989-12-31’;

select stu_name, stu_sex, stu_birth
from tb_student
where stu_birth between ‘1980-1-1’ and ‘1989-12-31’;

– 标准SQL的做法
select
stu_name as 姓名,
case stu_sex when 1 then ‘男’ else ‘女’ end as 性别,
stu_birth as 生日
from tb_student
where stu_birth between ‘1980-1-1’ and ‘1989-12-31’;

select stu_name,
case stu_sex when 1 then '男’else ‘女’ end,
stu_birth from tb_student where stu_birth between ‘1980-1-1’ and ‘1989-12-31’;

– MySQL方言 if() 函数 —> Oracle方言 decode() 函数
select
stu_name as 姓名,
if(stu_sex, ‘男’, ‘女’) as 性别,
stu_birth as 生日
from tb_student
where stu_birth between ‘1980-1-1’ and ‘1989-12-31’;

– 查询姓“杨”的学生姓名和性别(模糊)
– 通配符（wildcard）—> % —> 匹配零个或任意多个字符
select stu_name, stu_sex from tb_student where stu_name like ‘杨%’;

– 查询姓“杨”名字两个字的学生姓名和性别(模糊)
– 通配符（wildcard）—> _ —> 精确匹配一个字符
select stu_name, stu_sex from tb_student where stu_name like ‘杨_’;

– 查询姓“杨”名字三个字的学生姓名和性别(模糊)
select stu_name, stu_sex from tb_student where stu_name like ‘杨__’;

– 查询名字中有“不”字或“嫣”字的学生的姓名(模糊)
select stu_name from tb_student
where stu_name like ‘%不%’ or stu_name like ‘%嫣%’;

select stu_name from tb_student where stu_name like ‘%嫣%’
union
select stu_name from tb_student where stu_name like ‘%不%’;

– 基于正则表达式的模糊查询
select stu_name from tb_student where stu_name regexp ‘[杨林].{2}’;

– 查询没有录入家庭住址的学生姓名(空值)
select stu_name from tb_student
where stu_addr is null or stu_addr=’’;

select stu_name from tb_student
where stu_addr<=>null or stu_addr=’’;

– 查询录入了家庭住址的学生姓名(空值)
select stu_name from tb_student
where stu_addr is not null and stu_addr<>’’;

select stu_name from tb_student where stu_addr is not null and stu_addr<>’’;

– 查询学生选课的所有日期(去重)
select distinct sel_date from tb_record;

– 查询学生的家庭住址(去重)
select distinct stu_addr from tb_student
where stu_addr is not null;

– 查询男学生的姓名和生日按年龄从大到小排列(排序)
– 升序（从小到大）—> ascending
select stu_name, stu_birth from tb_student
where stu_sex=1
order by stu_birth asc;

– curdate —> 获取当前日期
– datediff —> 计算时间差（以天为单位）
– floor / ceil —> 向下/上取整
select
stu_name,
stu_birth,
floor(datediff(curdate(), stu_birth)/365) as stu_age
from tb_student
where stu_sex=1
order by stu_age desc;

select stu_name,stu_birth,
floor(datediff(curdate(),stu_birth)/365) as stu_age
from tb_student where stu_birth order by stu_age desc;
– 降序（从大到小）—> descending
select stu_name, stu_birth from tb_student
where stu_sex=1
order by stu_birth desc;

– 查询年龄最大的学生的出生日期(聚合函数)
select min(stu_birth) from tb_student;
select min(stu_birth) from tb_student;

– 查询年龄最小的学生的出生日期(聚合函数)
select max(stu_birth) from tb_student;

– 查询编号为1111的课程考试成绩的最高分
select max(score) from tb_record where cou_id=1111;

– 查询学号为1001的学生考试成绩的最低分
select min(score) from tb_record where stu_id=1001;

– 查询学号为1001的学生考试成绩的平均分
select avg(score) from tb_record where stu_id=1001;
select sum(score) / count(score) from tb_record where stu_id=1001;

– 查询学号为1001的学生考试成绩的平均分，如果有null值，null值算0分
select sum(score) / count(*) from tb_record where stu_id=1001;
select avg(ifnull(score, 0)) from tb_record where stu_id=1001;

– ifnull —> 如果遇到null（空值），将其替换为指定的值

– 查询学号为1001的学生考试成绩的标准差
select std(score) from tb_record where stu_id=1001;

– 查询男女学生的人数(分组和聚合函数)
select
if(stu_sex, ‘男’, ‘女’) as 性别,
count(*) as 人数
from tb_student group by 性别;

select
if(stu_sex, ‘男’, ‘女’) as 性别,
count(*) as 人数
from tb_student group by stu_sex;

– 查询每个学院男女学生人数
select
col_id as 学院编号,
if(stu_sex, ‘男’, ‘女’) as 性别,
count(*) as 人数
from tb_student group by col_id, stu_sex;

– 查询每个学生的学号和平均成绩(分组和聚合函数)
select
stu_id as 学号,
round(avg(score), 2) as 平均分
from tb_record group by stu_id;

– 查询平均成绩大于等于90分的学生的学号和平均成绩
select
stu_id as 学号,
round(avg(score), 2) as 平均分
from tb_record
group by stu_id
having 平均分>=90;

– 查询1111、2222、3333三门课程平均成绩大于等于90分的学生的学号和平均成绩
select
stu_id as 学号,
round(avg(score), 2) as 平均分
from tb_record
where cou_id in (1111, 2222, 3333)
group by stu_id
having 平均分>=90;

– 分组以前的数据筛选使用where子句，分组以后的数据筛选使用having子句

– 查询年龄最大的学生的姓名(子查询)
set @a=(select min(stu_birth) from tb_student);

select @a:=(select min(stu_birth) from tb_student);

select @a;

select stu_name from tb_student where stu_birth=@a;

– 嵌套查询：把一个select的结果作为另一个select的一部分来使用
– 嵌套查询通常也称之为子查询，在查询语句中有两个或多个select
select stu_name from tb_student
where stu_birth=(
select min(stu_birth) from tb_student
);

– 查询选了两门以上的课程的学生姓名(子查询/分组条件/集合运算)
select stu_name from tb_student
where stu_id in (
select stu_id from tb_record
group by stu_id having count(*)>2
);

– 查询学生的姓名、生日和所在学院名称
select stu_name, stu_birth, col_name
from tb_student, tb_college
where tb_student.col_id=tb_college.col_id;

select stu_name, stu_birth, col_name
from tb_student t1 inner join tb_college t2
on t1.col_id=t2.col_id;

select stu_name, stu_birth, col_name
from tb_student natural join tb_college;

– 查询学生姓名、课程名称以及成绩(连接查询/联结查询)
select t2.stu_id, stu_name, t3.cou_id, cou_name, score
from tb_record t1, tb_student t2, tb_course t3
where
t1.stu_id=t2.stu_id and
t1.cou_id=t3.cou_id and
score is not null;

select stu_name, cou_name, score
from tb_student t1 inner join tb_record t2
on t1.stu_id=t2.stu_id inner join tb_course t3
on t2.cou_id=t3.cou_id where score is not null;

select stu_name, cou_name, score
from tb_student natural join tb_record natural join tb_course
where score is not null;

– 分页查询
select stu_name, cou_name, score
from tb_student natural join tb_record natural join tb_course
where score is not null
order by score desc limit 5;

select stu_name, cou_name, score
from tb_student natural join tb_record natural join tb_course
where score is not null
order by score desc limit 5 offset 5;

select stu_name, cou_name, score
from tb_student natural join tb_record natural join tb_course
where score is not null
order by score desc limit 5 offset 10;

select stu_name, cou_name, score
from tb_student natural join tb_record natural join tb_course
where score is not null
order by score desc limit 10,5;

– alter table tb_record change column stu_id sid int unsigned not null;
– alter table tb_record change column cou_id cid int unsigned not null;

– 查询选课学生的姓名和平均成绩(子查询和连接查询)
select stu_name, avg_score
from
tb_student t1,
(
select stu_id, round(avg(score),1) as avg_score
from tb_record group by stu_id
) t2
where t1.stu_id=t2.stu_id;

– 查询学生的姓名和选课的数量
select stu_name, total
from
tb_student t1,
(
select stu_id, count(*) as total from tb_record
group by stu_id
) t2
where t1.stu_id=t2.stu_id;

– 查询每个学生的姓名和选课数量(左外连接和子查询)
– 内连接：查询左右两表满足连接条件的数据。
– 外连接
– 左外连接：确保左表（现在join前面的表）中的所有记录都能查出来，不满足连接条件的补充null。
– 右外连接：确保右表（现在join后面的表）中的所有记录都能查出来，不满足连接条件的补充null。
– 全外连接：确保左表和右表中的所有记录都能查出来，不满足连接条件的补充null。

– 左外连接
select stu_name, ifnull(total, 0) as total
from tb_student t1 left outer join (
select stu_id, count(*) as total from tb_record
group by stu_id
) t2 on t1.stu_id=t2.stu_id;

– 删除tb_record表的外键约束
alter table tb_record drop foreign key fk_record_stu_id;
alter table tb_record drop foreign key fk_record_cou_id;

– 给tb_record表加两条记录，学号5566在学生表没有对应的记录
insert into tb_record
values
(default, 5566, 1111, ‘2019-09-02’, 80),
(default, 5566, 2222, ‘2019-09-02’, 70);

– 右外连接
select t1.stu_id, stu_name, t2.stu_id, total as total
from tb_student t1 right outer join (
select stu_id, count(*) as total from tb_record
group by stu_id
) t2 on t1.stu_id=t2.stu_id;

– MySQL不支持全外连接
– 可以通过左外连接与右外连接求并集运算得到全外连接的结果
select t1.stu_id, stu_name, t2.stu_id, total as total
from tb_student t1 left outer join (
select stu_id, count() as total from tb_record
group by stu_id
) t2 on t1.stu_id=t2.stu_id
union
select t1.stu_id, stu_name, t2.stu_id, total as total
from tb_student t1 right outer join (
select stu_id, count() as total from tb_record
group by stu_id
) t2 on t1.stu_id=t2.stu_id;