根据参考， code> SET 字段使用一个字节最小，所以这些出口为任何种类的合并。

According to the reference, SET fields use one byte minimum so those are out for any kind of merging.

更新： ENUM 也是：​​它们至少也需要一个字节。 参考

Update: ENUM is out, too: They take at least one byte as well. Reference