To enforce the uniqueness we only allow mapping of each unique/primary key value to one partition.
If we removed this limitation it would mean that for every insert/update we need to check in every partition to verify that it is unique. Also PK-only lookups would need to look into every partition.
What could be done is to enhance partitioning with Global Indexes, so that the unique/primary key is partitioned by those fields (or not partitioned at all) and the rest of the data are partitioned on a field not part of the unique/primary key. But this would mean that dropping a ‘data‘ partition would need to do row-by-row deletes in the unique/primary key partitions/index. Also a PK-only lookup which accesses the whole row would need two lookups, the first on the PK index, and then on the ‘data‘ index to retrieve the rest of the row.
mysql分区表存在唯一索引时，唯一索引为什么必须包含所有分区字段
原文：https://www.cnblogs.com/cnsr/p/13268753.html