sql script how to get bigger value from list.

I've a table name User_detail, 1 user_id can have many level assign.

how can I set the level sequence in SQL witout setup table, and everytime when i want to display user level; it will always check from the sequence and display the higher value. my sequest is {1, 2, 3A, 3B, 5, AA, AB, 1A, 1B}

Example: UserA has level 1, 3A, AA, 1A So, when I display, I want to display 1A only for UserA