The users cannot see the indexes, they are just used to speed up queries.
用户并不会看见这些索引，它们仅仅让查询速度变快而已。
The two database systems support primary keys, along with key indices that allow you to speed up queries and constrain input.
这两个数据库系统都支持主键，以及支持加速查询和约束输入的键索引。
Indexes typically speed up queries, sometimes reducing the time required to execute the query to a fraction of the former elapsed time.
索引很好地加快了查询地速度，有时将执行的时间减少到以前占用时间的一小部分。
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