如何讀論文(三步法讀論文)
阿新 • • 發佈:2021-11-30
create database MySQlCrashCourse; use MySQlCrashCourse; create table Student( Sno char(9) primary key , Sname char(20) unique , Ssex char(2), Sage smallint, Sdept char(20) ); create table Course( Cno char(4)primary key , Cname char(40) not null , Cpno char(4), Ccredit smallint, foreign key (Cpno)references Course(Cno) ); create table SC( Sno char(9), Cno char(4), Grade smallint, primary key (Sno,Cno), foreign key (Sno)references Student(Sno), foreign key (Cno)references Course(Cno) ); insert into Course(Cno,Cname)value (1,'資料庫') ,(2,'數學') ,(3,'資訊系統') ,(4,'作業系統') ,(5,'資料結構') ,(6,'資料處理') ,(8,'PASCAL語言'); show databases; select *from Student; ## 查詢時間 select now(); ## 查詢當前使用者 select user(); ##建立索引 alter table 表名 add index 索引名(索引值) alter table Student add index ind_id(Sno); ##刪除索引 drop index ind_id on Student; ## 模糊查詢 select * from Student where Sno like 1; select * from Student where Sno not like 1; ## %替代多個字元 _替代單個字元 select * from Student where Sname like '_a%'; ## 查詢多個值 select *from Student where Sno in(201215121,201215122); ##別名 select Sno,concat(Sname,',',Ssex,',',Sdept)as site_info from Student; ## 內連線 select Student.*,SC.* from Student inner join SC on Student.Sno = SC.Sno; ## 左連線 select Student.*,SC.* from Student left join SC on Student.Sno = SC.Sno; ## 右連線 select Student.*,SC.* from Student right join SC on Student.Sno = SC.Sno; ##完全連線 select Student.*,SC.* from Student full join SC on Student.Sno = SC.Sno;