Oracle 10g Error: Warning: Trigger created with compilation errors - sql

Question

I have created database where I want autoincrement the primary key. I tried to trigger it but getting the above error
here is my description of table:
SQL> desc users
Name Null? Type
----------------------------------------- -------- ----------------------------
USER_ID NOT NULL NUMBER(8)
FIRST_NAME NOT NULL VARCHAR2(50)
LAST_NAME NOT NULL VARCHAR2(50)
CITY VARCHAR2(20)
COUNTRY VARCHAR2(20)
PASSWORD NOT NULL VARCHAR2(16)
EMAIL_ID NOT NULL VARCHAR2(50)
when I am trying to trigger it getting the error:
CREATE SEQUENCE SYSTEM.MYSEQ
2 START WITH 1
3 MAXVALUE 99999999
4 MINVALUE 1
5 NOCYCLE
6 CACHE 20
7 NOORDER;
CREATE OR REPLACE TRIGGER TR_USERS BEFORE INSERT ON USERS FOR EACH ROW
2 BEGIN SELECT LPAD(LTRIM(RTRIM(TO_CHAR(MYSEQ.NEXTVAL))),10,'0') INTO :NEW.USER_ID FROM DUAL;
3 /
please help me to solve this error.

Answer 1

You are getting the error, because you are missing the trigger's END:
CREATE OR REPLACE TRIGGER TR_USERS
BEFORE INSERT ON USERS
FOR EACH ROW
BEGIN
SELECT LPAD(LTRIM(RTRIM(TO_CHAR(MYSEQ.NEXTVAL))),10,'0')
INTO :NEW.USER_ID
FROM DUAL;
END; -- <=== this one
/
The trigger doesn't seem to make much sense, by the way. LPAD(LTRIM(RTRIM(TO_CHAR(MYSEQ.NEXTVAL))),10,'0') is just an obfuscated TO_CHAR(MYSEQ.NEXTVAL, 'FM0000000000'), but then, why create a string with leading zeros, when USERS.USER_ID is numeric??? You turn 123 into '0000000123' only to store it as 123.

Answer 2

There's nothing wrong with the trigger, as far as compilation is concerned (apart from the fact that you "forgot" to END it).
SQL> CREATE OR REPLACE TRIGGER TR_USERS
2 BEFORE INSERT ON USERS
3 FOR EACH ROW
4 BEGIN
5 SELECT lpad(ltrim(rtrim(to_char(myseq.nextval))), 10, '0')
6 INTO :new.user_id
7 FROM dual;
8 END;
9 /
Trigger created.
SQL> INSERT INTO USERS (FIRST_NAME) VALUES ('Little');
1 row created.
SQL> SELECT * FROM users;
USER_ID FIRST_NAME LAST_NAE CITY COUNTRY PASSW EMAIL_ID
---------- --------------- ---------- ---------- ---------- ----- --------------------
1 Little
SQL>
However, if USER_ID is NUMBER, you're overcomplicated trigger code because whatever you do with those functions, you'll - at the end - get just a number. As you can see from my example, USER_ID = 1.
If it were VARCHAR2, then
SQL> TRUNCATE TABLE users;
Table truncated.
SQL> ALTER TABLE USERS MODIFY user_id VARCHAR2(10);
Table altered.
SQL> INSERT INTO USERS (FIRST_NAME) VALUES ('Foot');
1 row created.
SQL> SELECT * FROM users;
USER_ID FIRST_NAME LAST_NAE CITY COUNTRY PASSW EMAIL_ID
---------- --------------- ---------- ---------- ---------- ----- --------------------
0000000002 Foot
SQL>
See the difference?
Trigger could've been simpler (but not much simpler; you're on 10g, after all) as there's nothing to trim:
SQL> CREATE OR REPLACE TRIGGER TR_USERS
2 BEFORE INSERT ON USERS
3 FOR EACH ROW
4 BEGIN
5 SELECT lpad(to_char(myseq.nextval), 10, '0')
6 INTO :new.user_id
7 FROM dual;
8 END;
9 /
Trigger created.
SQL> INSERT INTO USERS (FIRST_NAME) VALUES ('Krishna');
1 row created.
SQL> SELECT * FROM users;
USER_ID FIRST_NAME LAST_NAE CITY COUNTRY PASSW EMAIL_ID
---------- --------------- ---------- ---------- ---------- ----- --------------------
0000000002 Foot
0000000003 Krishna
SQL>

Answer 3

Apart from the missing end keyword, you don't need all the character formatting or the 'select from dual'. I would just use:
create or replace trigger tr_users
before insert on users
for each row
begin
:new.user_id := myseq.nextval;
end;
By the way, your sequence can also be written more simply as:
create sequence myseq;
Also, there is no need to code in uppercase. It's a bad habit from the 1970s.