6-Data update

insert data

SQL data insertion statement insert usually has two forms, inserting tuple and inserting sub-query results, the latter can insert multiple tuple at a time

insert tuple

Insert a new student ancestor

insert
into Student //The attribute name can be listed, the order can be different, but the values ​​should correspond to the attribute name order one by one
values ​​('16999010','Messi','Male',30,'CS');

Insert a course selection record

insert
into SC //Can write: SC(Sno, Cno), automatically assign NULL when the newly inserted record has no value
values ('16999010','1',NULL)

Insert subquery result

...

change the data

1. Change the age of student 16999010 to 22

update Student
set Sage=22
where Sno='16999010';

2. Increase the age of all students by 1 year

update Student
set Sage=Sage+1;

3. Set the grades of all students in the computer science department to zero

update SC
set Grade=0
where Sno in
(
    select Sno
    from Student
    where Sdept='CS'
);

delete data

1. Delete the student record whose student number is 16999010

delete
from Student
where Sno='16999010';

2. Delete all students' course selection records

delete
from SC; // will make SC an empty table, removing all tuples of SC

3. Delete the course selection records of all students in the Department of Computer Science

delete
from SC
where Sno in
(
    select Sno
    from Student
    where Sdept='CS'
);