Algorithm Question

[Lawrence D'Oliveiro]

In message <eeconn$s2n$1$8300dec7 at news.demon.co.uk>, Andrew McLean wrote:

> I have the ability to query a database in a legacy system and extract
> records which match a particular pattern. Specifically, I can perform
> queries for records that contain a given search term as a sub-string of
> a particular column.

What are the constraints on search terms? Are you allowed to specify the
null search term, which would match everything?