SQL TRIGGERS PROGRAM IN SQL

Initially create a student database table named student18 and then enter the values
then  start
SQL> select * from student18;

    ROLLNO NAME                           SUBJECT                SEMESTER

---------- ------------------------------ -------------------- ----------

         2 SANKET2                        WDP                           2

         3 SANKET3                        DCN                           2

         4 SANKET4                        MMC                           2

SQL> desc student18;

 Name                                      Null?    Type

 ----------------------------------------- -------- ----------------------------

 ROLLNO                                             NUMBER(38)

 NAME                                               CHAR(30)

 SUBJECT                                            CHAR(20)

 SEMESTER                                           NUMBER(38)

SQL> alter table student18

  2  add (DOJ date);

Table altered.

SQL> create or replace trigger trigstud

  2  before insert

  3  on student18

  4  for each row

  5  begin

  6  if :new.doj > sysdate then

  7  raise_application_error

  8  (-20002,' Date of joining cannot be after system date.');

  9  end if;

 10  end;

 11  /

Trigger created.

SQL> save string18;

Created file string18.sql

SQL> desc student18;

 Name                                      Null?    Type

 ----------------------------------------- -------- ----------------------------

 ROLLNO                                             NUMBER(38)

 NAME                                               CHAR(30)

 SUBJECT                                            CHAR(20)

 SEMESTER                                           NUMBER(38)

 DOJ                                                DATE

SQL> select sysdate from dual;

SYSDATE

---------

28-FEB-13

SQL> insert into student18 values(1,'sanket','dbms',2,'22-feb-2013');

1 row created.

SQL> insert into student18 values(5,'sanket5','dcn',2,'02-mar-2013');

insert into student18 values(5,'sanket5','dcn',2,'02-mar-2013')

            *

ERROR at line 1:

ORA-20002:  Date of joining cannot be after system date.

ORA-06512: at "SCOTT.TRIGSTUD", line 3

ORA-04088: error during execution of trigger 'SCOTT.TRIGSTUD'

SQL>  insert into student18 values(5,'sanket5','dcn',2,'02-feb-2013');

1 row created.

SQL> select * from student18;

    ROLLNO NAME                           SUBJECT                SEMESTER

---------- ------------------------------ -------------------- ----------

DOJ

---------

         2 SANKET2                        WDP                           2

         3 SANKET3                        DCN                           2

         4 SANKET4                        MMC                           2

    ROLLNO NAME                           SUBJECT                SEMESTER

---------- ------------------------------ -------------------- ----------

DOJ

---------

         1 sanket                         dbms                          2

22-FEB-13

         5 sanket5                        dcn                           2

02-FEB-13