Having fined-grained database tables means more table joins and accordingly more complex queries.
细粒度的数据表意味着更多数据表连接，相应的查询也会更复杂。
Writing SQL queries that use these more advanced table joins will be addressed in future articles.
编写使用这些比较高级的表连接的SQL查询将在后续文章中介绍。
Furthermore, querying decomposed XML data can be challenging, often requiring multi-table joins.
另外，查询分解的XML数据很困难，常常需要多表联结。
Learn about relational databases, data models, unique keys, primary keys, foreign keys, and table joins.
了解关系数据库、数据模型、惟一键、主键、外键和表联结。
This implicit association avoids database table joins and extra selections, and cuts down data transfer size.
这种隐式关联避免了数据库表连接和额外的字段选择，降低了数据传输的大小。
The entire fact table is read if all dimension table joins are removed by this optimization.
如果所有的维度表连接被该优化移除，则会读取全部事实表记录。
This is a particular case when one table joins to itself with one or two aliases to avoid confusion.
一个表联接自己时是一种特殊情况，为了避免混淆，采用一个或两个别名。
Design sane query schemas. don't be afraid of table joins, often they are faster than denormalization.
设计健全的查询模式。不要害怕表联合，通常它们比非范式化更快。
Relational queries, such as table joins, are possible, but they are implemented by multiple sequential queries.
关系查询（例如表连接）是允许的，但要通过多个连续查询才能实现。
In the absence of table joins, de-normalization is often used in HBase to keep related information in one table.
在缺乏表连接时，HBase通常使用去规范化(de - normalization)来将相关信息保存在一个表中。
As shown above, queries on concrete classes only select the required data without unnecessary table joins or unions.
正如上文所示，对具体类的查询只选择需要的数据，没有不必要的表连接和联合。
The approach generally fits well with a data warehouse system since all data is in one table without the need for table joins.
这种方法通常比较适合数据仓库系统，因为所有数据都在一张表里，不需要做表连接。
Is the duplication of data in multiple tables of frequently requested columns, more or less expensive than performing the table joins?
对于具有经常被请求的列的多个表，一种是复制其中的数据，一种是执行表连接，两者谁的成本更高呢？
This section focuses on selecting data from a single table; the last section in this article covers table joins and selecting data from multiple tables.
这一节将重点介绍如何从单表中选择数据；本文中的最后一节将介绍表连接和如何从多个表中进行选择。
This section focuses on selecting data from a single table; the last section in this article covers table joins and selecting data from multiple tables.
这一节将重点介绍如何从单表中选择数据；本文中的最后一节将介绍表连接和如何从多个表中进行选择。
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