Type alias Selection<DB, TB, SE>

Selection<DB, TB, SE>: [DB] extends [unknown]
    ? {
        [E in FlattenSelectExpression<SE> as ExtractAliasFromSelectExpression<E>]: SelectType<ExtractTypeFromSelectExpression<DB, TB, E>>
    }
    : {}

Turns a SelectExpression or a union of them into a selection object.