Invalid number while comparing string to number oracle - sql

Question

Hello I am currently involved in a project that is running for over 2 years, and yesterday, we started to face following issue:
One query that was always used and ran at least 20.000 every single day, yesterday fom nothing started to return invalid number error.
ORA-01722: invalid number
select orq.rt_id, orec.* from orderrec orec
join order_header oh on (oh.order_code = orec.ordernumber and oh.page = orec.pagenumber)
left join order_request orq on oh.orq_id = orq.orq_id
where ordernumber=? and pagenumber=? and state < 100
the problematic part is:
oh.order_code = orec.ordernumber
order_code is a string
ordernumber is a number
As this is would give a high impact on clients production I've change the equal comparison to a like find query bellow. After this change process started to work again without issue.
select orq.rt_id, orec.* from orderrec orec join order_header oh on (oh.order_code like orec.ordernumber and oh.page = orec.pagenumber) left join order_request orq on oh.orq_id = orq.orq_id
where ordernumber=? and pagenumber=? and state < 10
This query is a XML file used with a java program.
My doubt is why this would have happend?

Answer 1

I would check to see if the ORDER_CODE field, which you say is a string, contains any new values with non-digit characters (0-9) as that would be my guess as to the cause.
Even though your ORDER_CODE field is a string, when you join that field with a number field, Oracle will attempt to convert that string to a number (implicitly). You might as well be using the to_number() function on the ORDER_CODE field, because that is how it's actually being processed.
For instance, this query:
select *
from tablea a
join tableb b
on a.order_code = b.ordernumber
Will not return an error if ORDER_CODE contains values with only digits (0-9) and no letters.
But if it does contain at least one such value, boom, you get the error you describe.
It is true that you can use LIKE to avoid the error, but it will be unable to match rows where the ORDER_CODE has letters. Notice how in this example http://sqlfiddle.com/#!4/f00f91/1/0 '9A' won't match with 9, whereas '8' does match with 8.
The answer in a nutshell is that because you're joining two fields of a different format, one a string, one a number, a conversion from the string to a number is implied. And obviously, when the string contains letters such as A, B, C, etc. it will be unable to do the conversion and so it will give you that error.
You can run this query to find the "problem values", my guess is that whatever rows are returned were recently inserted, causing the error:
Fiddle:
http://sqlfiddle.com/#!4/f5b55/1/0
select *
from order_header
where regexp_like(order_code, '[^0-9]')