mysql的视图和连表查询案例

视图

• 创建视图

  • create view 视图名称

• 视图修改

  • create or replace view 视图名称 as 查询语句；

  • alter view 视图名称 as 查询语句

• 删除视图

  • drop view 视图名，视图名。。。。

• 查看视图

  • DESC视图名；——查看视图相关字段

  • SHOW CREATE VIEW 视图名； 查看视图

联表查询案例

• 查询" 01 "课程比" 02 "课程成绩高的学生的信息及课程分数

  • select * from t_mysql_students s, (select * from t_mysql_score where cid='01') t1, (select * from t_mysql_score where cid='02') t2 where s.sid=t1.sid and t1.sid=t2.sid and t1.score>t2.score;

    • 考点：多表查询

• ）查询同时存在" 01 "课程和" 02 "课程的情况

  • select * from t_mysql_studets s, (select * from t_mysql_score where cid='01') t1, (select * from t_mysql_score where cid='02') t2 where s.sid=t1.sid and t1.sid=t2.sid;

• -- 03）查询存在" 01 "课程但可能不存在" 02 "课程的情况(不存在时显示为 null )

  • select * from t_mysql_studens s inner jion (select * from t_mysql_score where cid='01') t1, on s.sid=t1.sid left join (select * from t_mysql_score where cid='02') t2 on t.sid=t2.sid;

• 查询不存在" 01 "课程但存在" 02 "课程的情况

  • select * from t_mysql_students s,t_mysql_score sc where s.sid=sc.sid and sid not in (select * from t_mysql_score where cid='01') and sc.cid='02'

• 查询平均成绩大于等于 60 分的同学的学生编号和学生姓名和平均成绩

  • select s.sid ,s.sname,avg(sc.score) n from t_mysql_studetns s left join t_mysql_score sc on s.sid=sc.sid group by s.sid,s.sname having n>60;

• 查询在t_mysql_score表存在成绩的学生信息

  • select * from t_mysql_students s inner join t_mysql_score sc on s.sid=sc.sid

• 查询所有同学的学生编号、学生姓名、选课总数、所有课程的总成绩(没成绩的显示为 null )

  • select s.sid ,s.sname,count(sc.score) ,sum(sc.score) from t_mysql_studets s left join t_mysql_score sc on s.sid=sc.sid gruop by s.sid ,s.sname;

• -- 08）查询「李」姓老师的数量

  • select count(tname) from t_mysql_teacher where tname like '李%'