Sql trigger not functioning - sql

Question

CREATE OR REPLACE TRIGGER STUDENT
BEFORE INSERT
ON STUDENT
FOR EACH ROW
BEGIN
IF :NEW.ENO =NULL THEN
RAISE_APPLICATION_ERROR(-21900, 'ENROLL_NO IS MISSING');
END IF;
END;
So this was my trigger definition
But when I try to NUll values its accepted
I'm learning

Answer 1

It is not = null, but is null:
SQL> CREATE OR REPLACE TRIGGER trg_bi_student
2 BEFORE INSERT ON STUDENT
3 FOR EACH ROW
4 BEGIN
5 IF :NEW.ENO is NULL THEN
6 RAISE_APPLICATION_ERROR(-21900, 'ENROLL_NO IS MISSING');
7 END IF;
8 END;
9 /
Trigger created.
SQL> insert into student (eno, name) values (1, 'Little');
1 row created.
SQL> insert into student (eno, name) values (null, 'Foot');
insert into student (eno, name) values (null, 'Foot')
*
ERROR at line 1:
ORA-21000: error number argument to raise_application_error of -21900 is out of
range
ORA-06512: at "SCOTT.TRG_BI_STUDENT", line 3
ORA-04088: error during execution of trigger 'SCOTT.TRG_BI_STUDENT'
SQL>
Though, why trigger? That's a not null constraint (most probably a primary key):
SQL> drop table student;
Table dropped.
SQL> create table student (eno number constraint pk_student primary key,
2 name varchar2(10));
Table created.
SQL> insert into student (eno, name) values (1, 'Little');
1 row created.
SQL> insert into student (eno, name) values (null, 'Foot');
insert into student (eno, name) values (null, 'Foot')
*
ERROR at line 1:
ORA-01400: cannot insert NULL into ("SCOTT"."STUDENT"."ENO")
SQL>
As of your second trigger (posted in a comment): if you show errors, then:
SQL> CREATE OR REPLACE TRIGGER TOTALMARKS
2 BEFORE INSERT ON STUDENT
3 FOR EACH ROW
4 BEGIN
5 :NEW.TOTAL: =:NEW.S1+:NEW.S2+:NEW.S3;
6 DBMS_OUTPUT.PUT_LINE('TOTAL="| | :NEW. TOTAL) ;
7 END;
8 /
Warning: Trigger created with compilation errors.
SQL> show err
Errors for TRIGGER TOTALMARKS:
LINE/COL ERROR
-------- -----------------------------------------------------------------
2/11 PLS-00103: Encountered the symbol " " when expecting one of the
following:
:= . ( # % ; indicator
SQL>
This is the 2nd line in excecutable part of the trigger:
:NEW.TOTAL: =:NEW.S1+:NEW.S2+:NEW.S3;
1234567890123456
^
|
11th character
It says that you should've used := and not : = (i.e. no space in between), but then you get another error:
SQL> CREATE OR REPLACE TRIGGER TOTALMARKS
2 BEFORE INSERT ON STUDENT
3 FOR EACH ROW
4 BEGIN
5 :NEW.TOTAL :=:NEW.S1+:NEW.S2+:NEW.S3;
6 DBMS_OUTPUT.PUT_LINE('TOTAL="| | :NEW. TOTAL) ;
7 END;
8 /
Warning: Trigger created with compilation errors.
SQL> show err
Errors for TRIGGER TOTALMARKS:
LINE/COL ERROR
-------- -----------------------------------------------------------------
3/22 PLS-00103: Encountered the symbol "TOTAL="| | :NEW. TOTAL) ;
END;" when expecting one of the following: (...)
You can't enclose strings into double quotes - use single ones. But, there's another error (consecutive pipe sign for concatenation), and yet another (no space between :new and .total), until finally it compiles:
SQL> CREATE OR REPLACE TRIGGER TOTALMARKS
2 BEFORE INSERT ON STUDENT
3 FOR EACH ROW
4 BEGIN
5 :NEW.TOTAL :=:NEW.S1+:NEW.S2+:NEW.S3;
6 DBMS_OUTPUT.PUT_LINE('TOTAL='|| :NEW.TOTAL) ;
7 END;
8 /
Trigger created.
SQL>