Prevent duplicate player characters from being created in DB

[MCrank]

Look at implemented UNIQUE INDEX
https://docs.microsoft.com/en-us/sql/relational-databases/indexes/create-unique-indexes?view=sql-server-2017

https://stackoverflow.com/questions/37635287/enforce-unique-constraint-on-email-field-using-asp-net-dapper-orm-contrib?noredirect=1

https://stackoverflow.com/questions/4707063/how-can-i-do-an-insert-where-not-exists