Depending on how you encode names and what you define as a "letter", many Korean last names are single characters (Lee: 이, Park: 박, Kim: 김), though they're usua

Depending on how you encode names and what you define as a "letter", many Korean last names are single characters (Lee: 이, Park: 박, Kim: 김), though they're usually transliterated into multiple letters (Oh, not O). Every Korean "character" has multiple "letters", but they treated as one entity most of the time (like Chinese characters). Personally, I wouldn't risk it and would just make single character lookups reasonably fast. I doubt the number of relevant records exceed 100k, so the savings shouldn't be significantly enough to bother with. However, I've seen worse things done with poorer justifications.