该索引要求主键的每一个值都必须是唯一的。
This index requires each value in the primary key to be unique.
为什么我们通常在删除主键创建索引？
Why do we usually create an index before dropping the primary key?
表必须具有相同的主键、唯一索引或唯一约束。
Tables must have the same primary key, unique index, or unique constraint.
索引并不只是为了主键或者唯一键。
Indexes are not just for the primary keys or the unique keys.
索引并不只是为了主键或者唯一键。
Indexes are not just for the primary keys or the unique keys.
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