There are usually ways to trick the RDBMS query optimizer into doing the "right" thing, even with border case queries like the one you show. I don't know about Oracle, but for Sybase the optimizer will use a generic weighting when it doesn't know the SARGS (search arguments) or when the SARGS are the result of functions or local variables (as is the case for bound variables via placeholders). If the index histogram is reasonable then the generated query plan is probably going to be quite reasonable - after all it's the same thing that happens when using stored procedures, and they work really well (with Sybase).
Michael
PS - we're drifting quite a long way from perl here...
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