Oracle数据库基本操作五——存储过程与触发器

时间:2021-06-21 05:08:28

 

4. 存储过程与触发器:

例7-1: (存储过程) 创建一个显示学生总人数的存储过程。

set serveroutput on
create or replace procedure student_count
as
p1
number(3);
begin
select count(*) into p1 from student;
dbms_output.put_line(
'学生总人数是:'||p1);
end;
/
execute student_count();

例7-2: (存储过程) 创建显示学生信息的存储过程STUDENT_LIST,并引用STU_COUNT存储过程。

set serveroutput on;
create or replace procedure student_list
ascursor select_hand is/*定义游标方便使用*/
select sno,rtrim(sname) as sname,ssex,sage,sdept,sclass from student;
begin
for i in select_hand loop
dbms_output.put_line(i.sno
||' '||i.sname||' '||i.ssex||' '||i.sage||' '
    ||i.sdept||' '||i.sclass); end loop;
STUDENT_COUNT();
end;
/
execute student_list();

例7-3: (存储过程) 创建一个显示学生平均成绩的存储过程。

set serveroutput on;

create or replace procedure student_avgs
(no
in student.sno%type)
as
avgs1
number(3,1);
begin
select avg(score) into avgs1 from score group by sno having sno = no ;
dbms_output.put_line(
'学号为:'||no||' 的平均成绩是:'|| avgs1);
end;
/
execute student_avgs('96002');

例7-4: (存储过程) 创建显示所有学生平均成绩的存储过程。

set serveroutput on
create or replace procedure student_avgs
as
cursor calcu_avgs is
select sno,avg(sno) as avgs from score group by sno;
begin
for i in calcu_avgs loop
dbms_output.put_line(
'学号为:'||i.sno||' 的平均成绩是:'|| i.avgs);
end loop;
end;
/
execute student_avgs();

例7-5: (修改数据库表) 在Student表中增加SAVG(N,6,2) 字段。

alter table student add savg number(6,2);

例7-6: (存储过程) 创建存储过程,计算每个学生的平均成绩保存到学生表SAVG字段中。

set serveroutput on
create or replace procedure save_savg
as
cursor calcu_avgs is
select sno, avg(sno) as ag from score group by sno;
begin
for i in calcu_avgs loop
update student set savg = i.ag where sno = i.sno;
end loop;
end;
/
execute save_savg();

 

例7-7: (触发器) 当更新学生成绩表SCORE中的学生成绩时,自动计算该学生的平均成绩保存到学生表SAVG字段中。

create or replace trigger TSTU_UPA
after
update or delete or insert on score
referencing new
as new old as old for each row
begin
if updating or inserting then
update student set savg=-1 where sno=:new.sno;
end if;
if deleting then
update student set savg=-1 where sno=:old.sno;
end if;
end;
/
create or replace trigger TSTU_UPS
after
update or delete or insert on student
declare
ssno
char(5);
ssavg
number(6,1);
begin
select sno into ssno from student where savg=-1;
select avg(score) into ssavg from score group by sno having sno=ssno;
if updating or inserting then
update student set savg=ssavg where sno=ssno;
end if;
if deleting then
update student set savg=ssavg where sno=ssno;
end if;
end;

 

例7-8: (触发器) 创建包含插入、删除、修改多种触发事件的触发器DML_LOG,对SCORE表的操作进行记录。用INSERTING、DELETING、UPDATING谓词来区别不同的DML操作。

先创建事件记录表LOGS,该表用来对操作进行记录。该表的字段含义解释如下:

    LOG_ID:操作记录的编号,数值型,它是该表的主键,自动增1,可由序列自动生成。

    LOG_TABLE:进行操作的表名,字符型,非空,该表设计成可以由多个触发器共享使用。比如我们可以为Student表创建类似的触发器,同样将操作记录到该表。

    LOG_DML:操作的动作,即INSERT、DELETE或UPDATE三种之一。

    LOG_KEY_ID:操作时表的主键值,数值型。之所以记录表的主键,是因为主键是表的记录的惟一标识,可以识别是对哪一条记录进行了操作。对于Score表,主键是由SNO_CNO构成。

    LOG_DATE:操作的日期,日期型,取当前的系统时间。

    LOG_USER:操作者,字符型,取当时的操作者账户名。比如登录SCOTT账户进行操作,在该字段中,记录账户名为SCOTT。

set serveroutput on;
create table logs(
log_id
number primary key,
log_table
varchar2(30),
log_dml
char(10),
log_key_id
varchar2(30),
log_date date,
log_user
char(30) );
create sequence log_id;
create or replace trigger sc_logs after insert or delete or update on score
referencing new
as new old as old for each row
declare
tlog_id logs.log_id
%type;
tlog_table logs.log_table
%type;
tlog_dml logs.log_dml
%type;
tlog_key_id logs.log_key_id
%type;
tlog_date logs.log_date
%type;
tlog_user logs.log_user
%type;
begin
select max(logs.log_id) into tlog_id from logs;
tlog_table :
= 'score';
tlog_date :
= sysdate;
tlog_user :
= user;
if inserting then
tlog_dml :
= 'insert';
tlog_key_id:
=:old.rowid;
insert into logs values(log_id.nextval, tlog_table, tlog_dml, tlog_key_id, tlog_date, tlog_user);
end if;