Is using "_" (underscore) safe?

const sq = this.db.$with('prods_with_qty').as(
      this.db
        .select({
          ...getTableColumns(ProductsTable),
          qty: SQL_PRODUCT_STOCKS_QTY,
        })
        .from(ProductsTable),
    );
this.db
        .with(sq)
        .select({
          ...sq._.selectedFields, // <- here. It's working perfectly fine, but should I do that?
          owner: SQL_USER_MINI_RES_COLS,
        })
        .from(sq)