重点：SQL查询公式的选择语句必须包括视图列中引用的全部字段。
Important: the Select statement of the SQL Query formula must include all the fields referenced in the view's columns.
如果批准的Web内容已经存在，那么负责改写决策阶段的人将决定只覆盖内容、覆盖全部字段，还是不执行覆盖。
If the approved Web content already exists, those who are responsible for the overwrite decision stage choose whether to overwrite content only, to overwrite all fields, or not to overwrite.
Covered索引在查询所请求的全部字段都包含在Covered索引中时能提升性能，因为不再需要取出完整的文档记录。
Covered indexes enhance performance when all fields requested by a query are contained within the covered index because there is no need to pull up the full document record.
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