Function join_using_output_schema 

pub fn join_using_output_schema(
    kind: JoinKind,
    left: &RowSchema,
    right: &RowSchema,
    using: &ResolvedJoinUsing,
) -> Result<RowSchema, SQLError>

Bind the visible and hidden output identities of a qualified join without constructing or executing the join. Static source-schema binding and the physical operator share this layout so an empty or correlated right side cannot lose its declared types.