Insert values except / merge

I'd like do be able to structure a query like: ```sql INSERT INTO <table> VALUES <values> EXCEPT SELECT <cols> FROM <table> ``` There might be a way to do this that I'm not sure of but some of the directions I went down were: ```swift db.insert(into: <table>).values(...).except(...) // Not an API db.insert(into: <table>).select(SQLSubQuery.select({ $0.values(...).union(...) // Not an API })) db.insert(into: <table>).select(SQLSubQuery.except({ $0.values(...) }).except(...) // Not an API ) ``` Context: My ultimate objective is to perform a [merge](https://www.postgresql.org/docs/current/sql-merge.html) but I know that is not general SQL so I'm trying to get as close an approximation I can with a single query.