小结：
1、唯一键必须包含分区函数中的所有字段；主键是唯一键的一种；
A PRIMARY KEY must include all columns in the table's partitioning function
22.6.1 Partitioning Keys, Primary Keys, and Unique Keys
This section discusses the relationship of partitioning keys with primary keys and unique keys. The rule governing this relationship can be expressed as follows: All columns used in the partitioning expression for a partitioned table must be part of every unique key that the table may have.
In other words, every unique key on the table must use every column in the table's partitioning expression. (This also includes the table's primary key, since it is by definition a unique key. This particular case is discussed later in this section.)
https://dev.mysql.com/doc/refman/8.0/en/partitioning-limitations-partitioning-keys-unique-keys.html