What's the best way to check if string a begins with string b?
Both a and b are coming from fields in a table.
Requirements:
* Either a or b might have special chars (such as '%') in them which
should NOT do anything special - they're just plain strings, not
regular expressions.
* a and b can be of arbitrary length (no fixed limits)
* Ideally, I'd like it to be transparent to the query engine, so that
it can use indexes. If both a and b are indexed, it's possible in
theory to use the index to do most of the work - but I can't come up
with a query that makes use of it.
