Index as varchar or numeric

Question

Hi:
I'm using a field that contains only digits (0..9) and will use this field as a primary key. Does it make any difference if the field is a varchar or a numeric? I do not plan on performing any mathematical operations on the field's value, so it would be easier to store & retrieve as a varchar. But is it quicker to assess a row based on a primary key which is numeric or varchar?
Thanks.
- Rolf.

Answer 1

You would, potentially, have to call TO_CHAR on the number when you wrote it out, but I would tend to just rely on implicit conversion there. Depending on how you are reading the XML response, you can probably get a numeric value back without doing any conversion.
I would have two primary functional considerations here
1) Is this a key that any human will ever use? If you are generating an invoice number, for example, someone may want to look up that invoice using the invoice number even though invoice number doesn't have any business meaning. Do the users think of this string in numeric terms? Or as a string? For example, do the users see value 1 as the same as 000001? Or would they prefer to always enter the "right" number of characters.
2) Data integrity- if non-numeric characters would be incorrect, the field should be a number. Otherwise, someone will end up writing alphabetical characters to the field.
Both of these would tend toward using NUMBER columns, unless users were really attached to the idea that it isn't invoice #1, it is invoice "000000001".
As secondary factors, numbers are more compact than strings, so performance is likely to be marginally better with numers rather than strings. By the same token, the table and index(es) are likely to cnosume less disk space when you use numbers. Performance here, though, should be a secondary consideration to functionality.
Justin
Distributed Database Consulting, Inc.
http://www.ddbcinc.com/askDDBC