1-1：
create table test1_student(sid char(12) not null,name varchar(10) not null , sex char(2) , age int,birthday date , dname varchar(30), class varchar(10))
1-2：
create table test1_course(cid char(6) not null,name varchar(40) not null,fcid char(6),credit numeric(4,1))
1-3：
create table test1_student_course (sid char(12) not null ,cid char(6) not null,score numeric(5,1),tid char(6),sctime date)
1-4：
Delete the wrong data before inserting it repeatedly
①delete from test1_student where age = 20
Then complete the sql query
② insert into test1_student values (201800020101,'Wang Xin','Female',21,to_date('19940202','yyyymmdd'),'Computer College','2010')
③ insert into test1_student values (201800020102,'Li Hua','female',20,to_date('19950303','yyyymmdd'),'Software College','2009')
1-5：
Correct mistakes on the basis of previous
①delete from test1_course where CID = 800002 and CREDIT=2
② insert into test1_course values(800002,'database',800001,2.5)
1-6：
Correct mistakes on the basis of previous
①delete from test1_student_course where TID = 200101
②insert into test1_student_course values (201800020101,300001,91.5,200101,to_date('2009-07-15 9-9-9','yyyy-mm-dd hh24-mi-ss'))
③insert into test1_student_course values (201800020101,300002,92.6,200102,to_date('2009-07-15 10-10-10','yyyy-mm-dd hh24-mi-ss'))