mysql查询语句

-- 查询所有学生的姓名和性别(条件运算)
select stuname as 姓名, case stusex when 1 then '男' else '女' end as 性别 from tb_student;
select stuname as 姓名, if(stusex, '男', '女') as 性别 from tb_student;

-- 查询姓"杨"名字两个字的学生姓名和性别(模糊)
select stuname, stusex from tb_student where stuname like '杨_';

-- 查询姓"杨"名字三个字的学生姓名和性别(模糊)
select stuname, stusex from tb_student where stuname like '杨__';

-- 查询没有录入家庭住址的学生姓名(空值)
select stuname from tb_student where stuaddr is null;

-- 查询课程编号为1111的课程的平均成绩(筛选和聚合函数)
select avg(score) from tb_record where cid=1111;

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