Check if VARCHAR2 contains only alphabets using trigger - sql

Question

I need to write such a trigger that will check name of the person and will print out his/her id if those people have any digits in theirs names.
What I have by now:
set SERVEROUTPUT ON
create or replace trigger BeforeUpdate
Before insert on customer
for each row
declare
n varchar2(10);
counter number;
nextR number:=0;
begin
select count(id_customer) into counter from customer;
LOOP
nextR:= nextR +1;
select cname into n from customer where id_customer = nextR;
if n not like '%[0-9]%' then
DBMS_OUTPUT.PUT_LINE(nextR || ' has incorrect name');
end if;
exit when nextR = counter;
end loop;
end;
/
It compiles and when I am trying to fire this trigger it do nothing.
I will be grateful for any help.

Answer 1

There are a couple of problems in your code:
using dbms_output in a trigger doesn't really make sense; usually, the INSERT will be performed by client code that doesn't handle the console output.
The sensible thing is to raise an exception instead.
You don't need to perform a SELECT in your trigger code. In fact, doing so will usually either be superfluous or raise a mutating table error. Instead, use :new and :old to refer to the values of the row that was inserted
(minor) naming a before insert trigger BeforeUpdate is somewhat confusing
use a regular expression for testing this business rule (seriously; regexes rule for this kind of thing)
Altogether, here's the fixed version (untested, I don't have an Oracle instance available for testing right now):
create or replace trigger TR_BI_CUSTOMER
Before insert on customer
for each row
begin
if regexp_like(:new.name, '.*[0-9].*') then
raise_application_error(-20001, 'Incorrect name: ' || :new.name);
end if;
end;

Answer 2

Use regular expression to get your result.
In your case, if you get a digit in n, your if clause should be executed.
So,
if regexp_replace(n,'[^[:digit:]]') IS NOT NULL then
DBMS_OUTPUT.PUT_LINE(nextR || ' has incorrect name');
end if
It seems you are also attempting to use a regular expression for digit. However, what your code is searching is for a string that has [0-9] in it. Like Bat[0-9]Man, which is not your desired result.
In my code, whatever expression is not digit in the given name is being replaced. If the name does not contain any digits, the regular expression would return null. If there is any digit at any place,the expression would return those digits.
You could analyse the following query for better grasping of what is happening here:
select regexp_replace(cname,'[^[:digit:]]') OUTP, cname from customer;
EDIT :
This is not how you write a trigger !
The trigger will be fired each time an insert is going to take place. You don't need the counter. You need to use :NEW reference
set SERVEROUTPUT ON
create or replace trigger update or
Insert on customer
for each row
begin
if regexp_replace(:NEW.cname,'[^[:digit:]]') IS NOT NULL then
DBMS_OUTPUT.PUT_LINE(nextR || ' has incorrect name');
end if;
end;
/

Answer 3

This is a job for REGEXP_LIKE()! The regex of '\d' matches a number.
SQL> with tbl(id, name) as (
select 1, 'Batman' from dual union
select 2, 'Robin1' from dual union
select 3, 'Supe4rman' from dual union
select 4, '3Joker' from dual
)
select id, name bad_name
from tbl
where regexp_like(name, '\d');
ID BAD_NAME
---------- ---------
2 Robin1
3 Supe4rman
4 3Joker
SQL>
If your goal is to strip out the digits on the way in (but be careful, a company really could have a number in the name like Level3 Communications or 3Com, if it's a person its less likely but these days who knows!) This is untested:
CREATE OR REPLACE TRIGGER customer_bu
BEFORE INSERT OR UPDATE
ON customer
REFERENCING NEW AS NEW OLD AS OLD
FOR EACH ROW
BEGIN
-- If the new name contains a digit, strip it.
if regexp_like(:new.name, '\d') then
:new.name := regexp_replace(:new.name, '\d', NULL);
end if;
END customer_bu;
/