To better illustrate the improvement in cardinality estimation, drop all the existing indexes on the EMPLOYEE table except the primary key index.

为了更好地解释说明基数估计值的提高，撤销除主键索引外的所有employee表上的现有索引。

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Also, before setting up replication in DB2, you will want to ensure that every database table has a primary key or unique index.

此外，在DB 2中创建复制之前，您会希望保证每一个数据库表都具有一个主键或惟一索引。

youdao

We keep only a compound primary key and a secondary index for each row, and answer all queries from a single index.

我们只保留了一个组合主键和一个辅助索引来完成所有的查询。

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