PL/SQL学习笔记（三）

 -----创建一个序列，再创建一个表（主键是数字），通过序列生成该表的主键值。
 create table mytb1(
        m_id number primary key,
        m_name varchar2(20) not null
 )
 create sequence myseq2
 start with 1001
 increment by 2
 nomaxvalue
 nocycle
 cache 20;

 declare
       i integer;
 begin
       i :=1;
       while i<=10 loop
       insert into mytb1 values(myseq2.nextval,'德玛西亚');
       i :=i+1;
       end loop;

 end;
 select * from mytb;
 ---创建表Student，其主键为数值类型：
 drop table student;
 create table student(
 Stu_id number(6) primary key,
 Stu_name varchar2(20) not null,
 Stu_score number(3,1)
 );
 ---编写一个pl/sql语句块将100条记录插入表中
 select * from user_sequences;  --查询当前用户下的所有序列

 begin
        for i in 1..100 loop
            insert into student values(myseq2.nextval,'德玛西亚',92.5);
        end loop;
 end;
 select * from student;

 ---编写一个pl/sql语句块计算表student的平均成绩，并打印
 declare
      rs number;
 begin
      select avg(Stu_score) into rs from student;
     dbms_output.put_line(rs);
 end;

 ---编写一个pl/sql语句块，打印所有学生信息，如果成绩字段为null，显示为“无”
 ---方法一：
 begin
     for stu in (select stu_id,stu_name, nvl(to_char(Stu_score),'无') stu_score from student) loop
             dbms_output.put_line(stu.stu_id||','||stu.stu_name||','||stu.stu_score);
     end loop;
 end;
 ---方法二
 select stu_id, stu_name,
     (
       case
                  when stu_score is null  then '无'
                  else to_char(stu_score)
       end
      ) stu_score
 from student;

 ---编写一个pl/sql语句块，打印成绩最高的20名学生信息
 delete from student where stu_score not like 'null';            --删除有成绩的学生记录

 begin
        for i in 1..50 loop
        insert into student values(myseq2.nextval,'Frank_Lei',trunc(DBMS_RANDOM.value(30,100),1));--插入30~100之间保留一位小数的随机成绩
        end loop;
 end;
 select * from student;

 declare
        cursor cur
        is
        select * from student where rownum<=20 order by stu_score desc;
 begin
        for stu in cur loop
            dbms_output.put_line(stu.stu_id||'...'||stu.stu_name||'...'||stu.stu_score);
        end loop;

 end;

 ---编写一个pl/sql语句块，打印所有学生信息，成绩显示为“合格”、“不合格”和“无”三种
 declare
        cursor cur
        is
        select * from student;
 begin
        for stu in cur loop
                case
                       when stu.stu_score<=0 then dbms_output.put_line(stu.stu_id||'...'||stu.stu_name||'...无');
                       when stu.stu_score>0 and stu.stu_score<60 then dbms_output.put_line(stu.stu_id||'...'||stu.stu_name||'...不合格');
                       else dbms_output.put_line(stu.stu_id||'...'||stu.stu_name||'...合格');
                end case;  

        end loop;
 end;

 ---利用一条sql语句实现上题功能
 select stu_id,stu_name,
        (
            case
                   when stu_score<=0 then '无'
                   when stu_score<60 and stu_score >0 then '不合格'
                   else '合格'
            end
        ) stu_score
 from student;

 ---编写一个pl/sql语句块，求阶乘
 declare
      temp number;
      rst number;
 begin
      temp :=1;
      rst :=1;
      while temp<=4 loop
            rst := rst*temp;
            temp :=temp+1;
      end loop;
      dbms_output.put_line(rst);
 end;